Solenochilus Meek & Worthen 1870 is one of a handful of prominently represented cephalopod genus found locally in the Brush Creek Limestone. One of it’s key features is a rapidly expanding whorl (Gordon 1964). Another is a pair of dorso-lateral spines at maturity (Mikesh 1966). In the seven specimens I have collected, I have found one, CG-0046, showing a short immature spine in good preservation on one side.

Another way to identify is identifying the siphuncle along the outside venter of the shell. It is located near the shell edge and is exposed when you have a steinkern.

Solenochilus Group Photo showing seven different specimens.
The seven local specimens of Solenochilus collected as of July of 2020.

How Solenochilus Obtained It’s Name

In April 1870, Meek & Worthen proposed a change of name for the then genus Cryptoceras. As you can see below, it’s not easy to simply change a name:

We propose the above name for a group of Nautili which we believe to be the same as Cryptoceras of D’Orbigny, published in 1850. This change of name becomes necessary, however, because Dr. Barrande had used the name Cryptoceras for another widely distinct group of Cephalopoda in 1846. It is true he has since changed the name of his genus to Ascoceras, for the reason that Latreille had applied the name Cryptocerus to a genus of Hymenoptera in 1804. But if Latreille’s name Cryptocerus is not considered sufficiently distinct, on account of its different termination, from Cryptoceras (which we should think is the case), it would, for the same reason, of course, be equally necessary to change the name of D’Orbigny’s group. On the other hand, if we regard Latreille’s name as being distinct enough to permit D’Orbigny’s name to stand also, or if Latreille’s genus is not a valid one, in either case Dr. Barrande’s original name Cryptoceras would have to be retained for his genus, and, as it has priority of date, it would still become necessary to find another name for the group described by D’Orbigny.

— F. B. Meek and A. H. Worthen of the Illinois State Geological Society
Proceedings of the Academy of Natural Sciences of Philadelphia

The reasoning continues on for another two paragraphs with further evidence and history to back their change of name. They placed Nautilus (Cryptoceras) Springeri as the type for the new group. In the original text, it appears they placed Solenochilus as a subgenus to the genus Nautilus. Naming is not done like that today, so it’s a bit confusing to read. I don’t see a family, superfamily, order or subclass listed.

The unproven holotype

The type specimen for the entire genus is said to be Nautilus (Cryptoceras) Springeri. It was named in Transactions of the Chicago Academy of Sciences in 1867, but only represented as an illustration.

Fig 10. Nautilus Springeri - 1867
Figure 10. The type specimen for Solenchilus, Nautilus (Cryptoceras) Springeri. The ear-like projection they mentioned could be the dorso-lateral spines.

Description of Nautilus (Cryptoceras) Springeri. by C.A. White and O.H. St. John

Shell moderately large, embracing; surface without conspicuous ornamentation; whorls somewhat rapidly increasing in size; outer chamber rapidy expanding towards the aperture, particularly toward the posterior and lateral margins; septa regularly convex towards the front; siphuncle small, dorsal.

Aperture large, subelliptical in outline, the margin of the front half of it forming an elliptic arch, but the outline of the posterior half is broken by the embraced inner coil, and also by the moderately prominent ear-like projection of the margin on each side, about half way between the inner coil and the middle of the lateral margin.

Tranverse diameter of the aperture eleven centimeters; from inner whorl to front margin six and a half centimeters.

Specific name given in honor of Frank Springer, Esq., of Columbus City, Iowa

Geological position and localities. Upper coal measures of Adair county, Iowa

Unique Views from specimen CG-0066

CG-0066 was the first specimen that allowed me to see the genus in cross-section. The underside shows three separate septal cross-sections, and a 4th if you include the aperture. Using a rock polishing wheel, I was able to polish this section to help bring out fine details in the chambers.

Solenochilus underside with illustrated septal lines
Specimen CG-0066 showing observed septal chamber cross sections from underside.

Solenochilus cf. S. peculiare Miller & Owen

This comes from Plate 12 in Geological Survey Professional Paper 460 by Mackenzie Gordon, Jr. One of the more interesting parts of his paper was an identification key to help a reader determine a species of Solenochilus by comparing some key morphological features. I hope to republish the key soon in a unique format.

In the photo below the siphuncle can be seen right above the number 12 as a vertical margin that interrupts the septal chambers.

Photo of USNM 119751 - S. peculiare Miller & Owen
Ventral and side views of an internal mold in sandstone, USNM 119751, from USGS loc. 16350, Atoka formation. Credit: U.S. Geological Survey / Department of the Interior/USGS

S. cambridgensis from the Conemaugh of Ohio

Stated as a new species in 1966, this one is found about 125 miles South West from Parks Township. Unique transverse crenulations on the body chamber along with unique size and morphology made the case for a new Solenochilus. The body chamber of paratype A (Specimen OSU 26789) was 263 mm.

If I were to take specimen CG-0025 and estimate a width from the center of the venter, I would only get 180 mm in width. The S. cambridgensis specimen is very large.

Solenochilus Specimens collected locally

IDPostUnique Feature
CG-0019SolenochilusFirst Found
CG-0025Solenochilus, probablyLargest Found
CG-0043Solenochilus II, with bite marksShark Bite Marks
CG-0046Solenochilus III, with lateral spinePreserved Lateral Spine
CG-0056Solenochilus IVLarge with several other specimens
CG-0066Solenochilus VClear inner whorl preservation
CG-0081Small SolenochilusSmallest Found