330 NEW YORK STATE MUSEUM 



tropidocycuus De Koninck. 1883 (emend. Clarke. 1899) 

 In the A rchivos do Musen National do Rio de Janeiro, 1899, 10:72 

 (39) * the writer made the following comments on this genus and its allies : 



In the Proceedings of the Chicago Academy of Sciences (1866, 1 :g) the 

 late Mr F. B. Meek introduced the name Tropidiscus for bellerophont 

 shells having the structure of B. curvilineatus Conrad, of the Cornif- 

 erous limestone ; that is, lentiform, sharply keeled and deeply involute 

 shells without expanded aperture or peripheral seam and with rather coarse 

 concentric growth wrinkles. The name proved to have been already in use, 

 and in a later publication of the same year 2 the author emended it to Tropi- 

 dodiscus and regarded a second species, there described as Bellerophon 

 cyrtolites Hall, from the Lower Carboniferous (Kinderhook) limestone, 

 as belonging to the same group. 



Later, De Koninck rejected Meek's term on the ground of preoccu- 

 pancy and introduced, to take its place, the name Tropidocyclus, 3 also 

 adopting B. c u r v i 1 i n e a t u s as the type of the group. This act was 

 not required by any law of nomenclature, and Mr Meek's name as emended 

 should stand as originally characterized by him. Of the three species which 

 De Koninck referred to his Tropidocyclus, none can be regarded as congen- 

 eric with Conrad's species. All are small, with broader and more expanding 

 body whorl, narrow umbilici and faint, lateral, revolving furrows, producing 

 a slightly trilobed exterior. The dorsal ridge is seamless, narrow and 

 pronounced, and the surface marked by fine, sharp, concentric, elevated 

 striae which follow the curvature of the peristomal margin, that is, are 

 sinuous on the lateral slopes and make a deep retral subangular curve on 

 the dorsum. 



The desirability of separating such forms as these from the peculiar 

 B. curvilineatus will, I believe, be admitted by students, and I there- 

 fore propose to adopt De Koninck's term, restricting it to such species as 

 he described. Of these, T. rotula 4 is the first in order, though I think 

 his T. gratiosus 5 better exhibits the characteristics of the group. These 

 shells differ from the Devonian species here referred to Bucaniella, in their 

 lateral appression, narrow dorsum, small umbilici and, conspicuously, in the 

 character of their ornamentation. 



'Molluscos devonianos do estado do Para, Brazil. 



2 Geological Survey of Illinois. Pal. 1866. 2:160. 



3 Faune du calcaire carbonifere de la Belgique. 1883. pt 4, p. 123. 



4(9/. cit. pi. 43, fig. 5 -8. 



5 Op cit. pi. 42 bis. fig. 44-48. 



