Ruth R. Mook — A New Cephalopod. 619 



The name proposed by Hall was printed in the second vol- 

 ume of the Paleontology of New York in 1850, although the 

 volume was not issued until 1852.* Hall's genotype was 

 Trochoceras gebhardi. His original description of the genus 

 follows : 



" Turbinate or trochiform ; spire elevated, more or less ven- 

 tricose, umbilicated ; aperture rounded or round oval ; volu- 

 tions above the outer one septate ; siphuncle submarginal or 

 dorsal. 



"In the specimen from which the generic description is 

 principally made, the septa are strongly arched from the inner 

 basal angle of the volution to the outer one, advancing on the 

 outer angle towards the aperture." In the above description 

 owing to a confusion of terms the siphuncle is recorded as sub- 

 marginal or dorsal, whereas in present day usage it would be 

 recorded as submarginal or ventral. 



In 1891 Hyatt pointed out that Hall's species are quite dis- 

 tinct from Barrande's, and that they do not belong to any 

 genus yet described from Bohemia. Trochoceras Barrande is 

 not generically identical with Trochoceras Hall. Hyatt sug- 

 gested that the name Trochoceras Barrande be retained and 

 for Hall's forms Trochoceras gebhardi and turbinatum he pro- 

 posed the new name Mitroceras with Mitroceras (7roch.) 

 gebhardi as the genotype. f Mitroceras Hyatt differs from 

 Trochoceras Barrande in the high turbinate spire, and in the 

 deep and sharply angulate umbilicus. 



Measons for assigning the new species under discussion to the 

 genus Trochoceras. 



The formation in which the specimen under discussion was 

 found has undergone little diastrophic movement. The beds 

 dip at an angle of about 40 degrees to the south, but outside 

 of uplifting and tilting there is no evidence of any great dis- 

 turbance such as twisting, mashing, etc. In the overlying 

 formation, the so-called Bastard limestone, fossils are abundantly 

 preserved and show no evidences of distortion. The speci- 

 men under discussion is considerably warped, apparently indi- 

 cating that it was a low spired trochoceracone rather than a 

 flat nautilicone ; its warped condition then can be reasonably 

 explained by the normal crushing of a cone-shaped shell. 



Trochoceras grovaniense sp. nov. 



Shell large, probably trochiform ; spire very slightly ele- 

 vated ; maximum diameter 158 mm ; diameter of outer whorl 



* Palaeontology of New York by James Hall ; vol. ii, p. 335. Albany, 



f Phylogeny of an Acquired Characteristic. Alpheus Hyatt. Proc. Amer. 

 Phil. Soc, vol. xxxii, No. 143, p. 502, 1894. 



