;i7(5 CARBONIFEROUS FORMATIONS AND KAUNAS oh' (U)LORADO. 



and divided by a sinus, neither Sowerby's nor Davidson's lif>ures ol' tlie type specnuien 

 sliow a sinus. Tlieir figures as well as their descriptions indicate that the hinge line 

 is no wider than the body of the shell. The ventral vahe seems not to have been 

 \(My highly arched, to judge by the figures, though Sowerby says that the "reflexed 

 margin is entirely lost, etc." riie ribs an' not mentioned in the original description 

 nor represented in the figures, but Davidson's figure shows them to be as prominent 

 as in the average specimen. They vary from 3U to o<i in number, according to this 

 author. Norwood and Pratten mention 30 as occurring in P. splendens. They are 

 usually more or less obsolete, however, and the sinus is typical!}^ deep and the ears are 

 produced. Freeh states that though related to P. Io!u/iynmti<. P. tij)lendenfi can 

 easily be distinguished by reason of its fainter striatiou and more strongly expressed 

 muscular and visceral markings. Waagen finds that typical specimens of P. loiuji- 

 spinus are practically entirely without the internal ridges characteristic of Margini- 

 fera, and according to his view, therefore, P. Jongispinus and P. splendens would be 

 found in different genera even. At all events it will be safe to conchide that they 

 are specifically distinct. 



Another species whose relationship with P. splendens is certainl}" close, and 

 whose name, in case of identitj^ proved, would supersede that proposed by Norwood 

 and Pratten, is P. capiaoii d'Orbigny. Waagen expresses the opinion that this species 

 is distinct from P. splendens, and with this I am content to agree, although, being 

 without specimens with which to make comparisons, a conclusive judgment can not 

 be formed. One difference manifest at first sight from the figures is the inflation of 

 the posterior portion of d'-Orbigny's shell b^y which it is brought to project far 

 bej'Ond the hinge line. In this particular P. capacii is close to Marginifeixi hayden- 

 etisis described below, which is certainly distinct from P. splendens. 



Turning now to the relationshiij of P. splendens and P. ^vabashejisis, one would 

 not long hesitate to conclude from Norwood and Pratten's figures that the two 

 species are clearlj^ distinct. Meek, however, after- examining good specimens of P. 

 wahashensis from the original locality, concludes (loc. cit.) that the figures of that 

 species are quite defective in representing the costee, and if one considers the 

 difference in proportion shown by the figures of the original reference between the 

 dorsal and ventral views of the same specimen, it seems clear that the outline, too, is 

 not to be trusted. 



1 have before me some specimens "from below the coal'' at Wabash cut-ofl', 

 New Harmony, Ind., which I suppose can be considered as coming from the original 

 locality and as representing the typical phase of P. wahashensis. Thej^ show a 

 broad, highly arched form, with strong median sinus and slightl}^ extended ears. 

 The beak is small and transgresses the hinge line but little. Concentric wrinkles 

 are almost wanting; the striee are fine and obsolescent, and the surface supports a 



