Ctenobactrites is a genus of cephalopod under the order of Bactritida, an order rarely found in Western Pennsylvanian rocks. Ctenobactrites differs from Bactrites only by having a coarse transverse lirae (Mapes 1979). While I have found these intact, I have yet to find a suitable steinkern for collection. This specimen lot came from the Pine Creek limestone, a fissile limestone that preserves shell material. Yet, the shells are fragile, breaking apart with ease. These are difficult to recover in one piece.

Ctenobactrites in-situ in Pine Creek limestone.
Ctenobactrites in-situ in Pine Creek limestone.

Identification of the specimen as the species Ctenobactrites isogramma (Meek 1871) is tentative. Bulletin 71, Pennylsvanian Cephalopods of Ohio lists only C. isogramma, and plates 1-9, 1-10, and 1-11 look to be congenic for this specimen. The bands increase in height as the specimen grew longer. The shell is orthoconic. Reports of the genus are rare in Pennsylvanian rocks of North America.

Several authors have searched for Meek’s physical holotype C. isogramma and came up empty-handed. Mapes (1979) erected Ctenobactrites for a specimen of Bactrites that had a sole coarse-banded patch of shell adhered to it.

Ctenobactrites isogramma
CG-0369 – Ctenobactrites isogramma fragments. These are shells from at least two different creatures.

I have mistaken this genus for fragments of bivalves in the past. The coarse ornament can resemble growth lines on a bivalve. The fragments also superficially resemble portions of a gastropod shell. But, they fail the test upon closer examination. I recovered a wider curved piece on a previous field trip and have also integrated it with CG-0369 as a lot.

Subgenera of Ctenobactrites

Shimansky (1954) erected subgenera, yet Mapes (1979) observed that some of the characteristics, such as rounded or flattened lirae, both exist in particular specimens, thus subgenera usage is not advised. The specimens above are an example of flattened lirae.

References