INVERTEBRATE PALAEONTOLOGY. 301 



row, very much depressed, the last one sharply angular around the periphery, 

 and obtusely subangular around the umbilicus; aperture transversely rhombic; 

 lip thin and simple; surface cancellately striated in the typical species. 



This genus was originally proposed by us for the reception of a small 

 shell described by Evans and Shumard under the name Solarium jlexistri- 

 atum. We originally separated it from Solarium mainly on account of the 

 pearly nature of its inner layer. At that time, we also thought it might also 

 include several of the depressed or subdiscoidal shells, with acutely-angular 

 periphery, a large, open umbilicus, and transversely-rhombic aperture, 

 described from the Cretaceous rocks, by d'Orbigny and others, under the 

 names Solarium orhatum, Fitton, S. dentatum, S. granosum, &c., d'Orbigny. 

 Since that time, however, better specimens of our type have been found, that 

 show the margin of its umbilicus not to be eremite (another distinction from 

 Solarium); while the foreign Cretaceous forms alluded to show, in part at 

 least, a tendencv to become crenate around the middle of the under side 

 (which may be regarded as the margin of the umbilicus), though in a very 

 different way from what we see in Solarium proper. Those shells also ditfer 

 from our type in being covered with coarse granules. Whether these differ- 

 ences should exclude them entirely from association with our type may admit 

 of some doubt; but, at any rate, it seems to me that such forms are clearly 

 distinct both from Solarium and Solariel/a. 



Dr. Stoliczka very positively asserts that our Margaritella ••must be 

 considered ;is synonym of So/arie/la" of Wood, 1842. In this, however, the 

 doctor was certainly too hasty. If he had seen our type-species, or read 

 Evans and Shumard's description of it attentively, he would have seen at 

 once that it differs very materially from the type of Wood's genus. On the 

 contrary, however, he seems to have formed hisideasof our genus from two 

 or three Cretaceous shells referred to it by Mr. Gabb in his California reports. 

 Like Dr. Stoliczka, however, Mr. Gabb had an incorrect impression of our 

 genus, (the type of which had not been figured at that time), and was wrong 

 in referring these California shells to it. Any one who will take the trouble 

 to compare our figures and description of the type-species of Margaritella, 

 will at a glance see that it is in all respects widely distinct from Solariella 

 maculata, Wood, the type of his genus; which is a subglobose shell, with 

 rounded volutions, and a distinctly crenate margin around its umbilicus. 



I agree with Dr. Stoliczka, however, that Solariella is clearly separated 



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