CAUHOXIFEIIOUS A(J K. 19 



generic group, to which Kimig gave the 11:11111- Tri<jiitrtl^, subsequently adopted 

 liy Trot'. Bronn, :ind \>\ Prof. King. 1 



\- lii-n- <li 'lined and t> pitied, it will lie seen that tlii^ i;eiiii- inelndo two rather 

 marked sections, with one or more le.>s distinctly detined groups, \shich maybe 

 characterised as follows: 



1. Spirifer (proper), SUWUBT, Cyrtla, DALMAIC, and othert. 



SI,. -11 trigonal, nearly always cosUte or strlate ; hinge generally a little lest than the breadth of the valves, 

 more or less angular at the extremities ; ventral valve very prominent or pyramidal ; beak straight or a 

 little . iir. . I ; ara Urge and triangular; foramen closed by a fale dvltidium, generally pierced by a imall 

 round or oral aperture near the apex of the beak ; dorsal valve comparatively compressed, semicircular. 



'. Trieoiiotrt-tn, Kouuo, ftpirifcr, of most authors. 



S1..-11 usually with both valves convex, marked as In the fort-going; lateral extremities generally angular, 

 often acutely so ; hinge line usually extended. Roth valves with beaks more or leas incurved ; area 

 variable in size, but rarely if ever so extravagantly developed as In some of the typical Spirifen ; foramen 

 open or more or lens closed by a false deltldinm without a perforation. 



J-'.rumple. pirif<r ilriatui, SowxBBT. 



8. Murtjnia, McCoy, Amboratia, HALL. 



Mi. II snbgloboae, or transversely or longitudinally oval, smooth or rarely with compressed rounded OOHUB; 

 often beset with minute hair-like spines. Hinge short, scarcely ever equalling the greatest transverse 

 diameter of the valves; lateral margins rounded, or rarely obtusely angular; beak of ventral valve 

 incurved ; cardinal area comparatively small ; foramen, and false deltidlnm as in Triyonolrela. 

 Type. $pirif< r ylabrr, SOWEBBT. 



The genus A)Y//I ///< of D'Orhigny, is also often considered a subgcnus under 

 >/////;/. The coincidence, however, of a punctate structure in these shells, with 

 the presence of a prominent mesial septum in the ventral valve, would seem to 

 indicate important differences in the structure of the animal, such as would warrant 

 its separation as a distinct genus.* So also with Ci/rliini of Davidson, which was 

 formerly included with the forms we here regard as the typical Spirifcrs, tinder the 

 name ( ';/rt'i. Mr. Davidson has, however, very properly separated these shells, on 

 account of their punctate structure, and the peculiar development of the dental 

 laminae of the ventral valve, which are produced inwards, and coalesce into a single 

 me-ial septum, extending from the extremity of the beak, almost to the anterior 

 margin, thus giving the interior more the appearance of Pt-ntamerus than Spirifer. 

 As Mr. Hillings has, however, discovered internal spiral appendages in one of these 

 shells, and they all possess a well-developed cardinal area, we cannot doubt the 

 propriety of including them in the A///V/A riitn , though we think, as above stated, 

 that they should constitute a distinct genus from all the other groups. 



As thus freed from the punctate species, the typical Spirifers (= Cyrtui, Dalman) 

 are found to pass by such insensible gradations into the Trigonotreta group (= the 



In his valuable work on the Permian fossils of England, Prof. King regarded Spirifer cuspidatus 

 as the type of the genus, and adopted Kocnig's name Trigonutreta for the shells generally considered 

 typiml Spirifers. It is said, however, that he subsequently changed his views in regard to the type 

 of Spirifer. 



1 I avail myself of this opportunity to refer to the genus Sfririferina, a species described by me 

 timli-r the name of Spirifera pulchra (Proi-cod. Acini. Nat. Sci. July, I860, p. 310), brought liy 

 Ciipt. Simpson from Nevada Territory. Sections of it show very distinctly a coarsely punctate, very 

 flm-ly fibrous structure; while casts of the interior exhibit a deep slit left by the mesial septum in the 

 l>cak of the ventral valve F. B. M. 



