>IIM>A 



867 



have an extravagant development of the delicatf j,'rano-lineate extension of the 

 iniHM h|> which i> tin- principal difference between /' "hi" and \\'tirllii>i. 



'I'li. point- linuight out in the foregoing paragraph an- significant and indicate, 

 we believe, that <hirnell<i and rnitoiftirtliiii. followed hy some Trtrtintii-\\ko type, 

 were important stages in the development of Itfllrrnplton. The types named are 

 .>l>viously progressive. The first has no slit-bund and only a very shallow sinus, the 

 second is still without the band but has a broad and deep sinus, while the thin! and 

 f.mith have a narrow and very deep parallel-sided sinus or slit which with the 



.\th of the shell causes the formation of a slit-band. 



IIKI.I .v. Waagen. (Pal. Indica, ser. 18, pt 2. PP . 132, 171; 1880.) Shells 

 agreeing in all respects with Mlrrnphon excepting that they are smoother and some- 

 what unsymmetrically coiled, there being an umbilicus on one side and none, or at 

 any rati a shallow one, on the other. Type, .S'. bifrons Waagen. 



So far as known no shells of this type have yet been found in American deposits. 

 Two species occur in the Permo-Carboniferous of India, and five in the Permian of 



\ '.p-. 'I'll.- latter are described by Stache in his monograph of the fauna of the 

 r.|loroj>hon limestone. Regarding the genus, it seems to mark an important 

 departure from the ordinary types of the family. We suspect that Sbirhelhi may be 

 the radical of the ophisthobranchs, but this is a mere suggestion. The Cretaceous 

 liellfrophina, d'Orbigny, is a similarly unsymmetrical shell, but has no slit-band and 

 only a shallow omar^i nation of the outer lip. 



Family CARINAKOPSII' 



1 1 metrical, almost patelliform shells, the .aperture being greatly expanded; 

 apex small, involute, overhanging the posterior margin, consisting of no more than 

 volutions. Within the aperture abroad concave septum. Anterior lip with a 

 'nil eniar^rination. 



This family embraces a small group of Lower Silurian shells that is readily dis- 

 tinguished from other bellerophontids by the internal septum. \Ve believe that it 

 should include also the genus Pftrotheca, which is now almost universally referred 

 to the / \ li-cussion of the affinities of this genus will he found under 



Carinaropsif. 



CAKUTAROPSIS Hull.* (PAruyMMtaNo, H*U,-| not Waagen.J) Shell consisting of 

 little more than two volution-, the inner one very small, scarcely embraced by the 

 outer, and shown in the umbilicus; outer volution greatly expanded, the whole shell 

 appearing somewhat patelliform: dorsum carinate, the carina sharp on the inner 



w York. TO), l. p. HO. 

 PourtN-nth (Up. X. Y. 8u Mum. Nat. HIU p. M : 

 t Plwotololc. Indlc*. wr. U pi. 2. p. 1X1; MM. 



