DESCKIPTIONS OF SPECIES. 391 



ornamentation, but certainly tliis analogy is of no importance in view of the diver- 

 sity that exists between the characteristic structure of the shell surface of these 

 species and that of the Sguamularise. As regards their internal characters, the 

 spiral cones of the Reticularise- ordinarily have the apex directed toward the hinge 

 line, and in the species in which it is turned sideways, as in the Squamularice, the 

 crura do not form an elbow, but, on the contrary, have very nearly the same direction 

 as in Mhrtinia; that is to sa}', the}' converge dii-ectly toward the median line, leaving 

 in the internal infra-apical region a larger or smaller triangular space, and the 

 descending laminae do not run parallel for a long distance, but, having approached 

 each other, suddenly diverge toward the sides, and give rise to the spiral cones. 



These fossils belong to two species, to which I have given the names of Squam- 

 ularia rotundata Gemm. and Squamularia dieneri Gemm. 



The Squamularia^ were found in the compact Fusulina limestone of the Rock of 

 San Benedetto, in the vicinity of Palazzo- Adriano, in the province of Palermo. 



The first species described, which must be taken as the type, is Squamularia 

 rotundata Gemm., and upon its characters accordingly rests the A'alidity of Gem- 

 mellaro's genus. It is quite evident that this author did not apprehend the more 

 obvious differences which distinguish Reticularia from his species of Squamularia, 

 and that he considered McCoy's genus to be devoid of dental lamellse and septa. If 

 the characters b}^ which he sought to distinguish Squamularia from Hetictdaria are 

 valid, there can be no doubt but that the forms referred by him to Heticidaria 

 constitute a yet undescribed genus. But I verj' much doubt the importance of the 

 characters to which Gemmellaro calls attention, and believe that the real characters 

 of distinction are the septa and dental plates which are present in Reticularia and 

 absent in Squamularia. This opinion seems to be confirmed by Schellwien, who 

 regards Squamidaria as a synonj'ui of Heticularia, the latter name evidentlj^ being 

 employed in the sense in which Waagen and Hall and Clarke interpret it. 



To Sqvmnularia, therefore, would belong all of Waagen's species of Reticulata 

 and also those of Gemmellaro himself, together probably with most American, 

 European, and Asiatic Upper Carboniferous types that have been included by authors 

 under McCoy's genus. More specifically with regard to our American species, 

 Squa/mularia will include only, so far as I know, the two Upper Carboniferous 

 forms Recticidaria perplexa McChesney and Reticularia guadahupensis Shumard, 

 both of which I have examined and know to be without septa or dental lamellas. 



To Reticularia will belong the Mississippian species R. clara Swallow (?), R. 

 cooperensis Swallow, R. lineatoides Swallow (?), R. pseudolineata Hall, R. setigera 

 Hall, R. temeraria Miller (?), R. tenuispinaf a Herrick, and R. trandata Swallow (?). 

 These Mississippian forms are usually characterized by two powerful dental plates 

 in the ventral valve, and a median septum in both dorsal and ventral valves. The 

 dorsal septum varies in degree, being sometimes low and sometimes moderatel}^ high. 



