294 PALEONTOLOGY OF NEW YORK. 



The structure of the articulating apparatus is the essential basis of distinc- 

 tion between this fossil and Plectambonites, but there is also no trace of 

 the characteristic muscular scars of the latter genus. There can be little 

 doubt that tlie species Leptana decipiens, Billings, from the same formation and 

 locality, belongs to the genus Leptella. Without having had access to the 

 original specimens, the figure given by Mr. Billtngs of the interior of a brachial 

 valve,* showing the double, erect cardinal process, the strong crural plates and 

 the concave visceral area, seems sufficient to determine this point. Precisely 

 similar features are shown in Davidson's figures of his species Leptena Llandeilo- 

 ensis,\ from the Upper Llandeilo of Ayrshire, and it may also be included in 

 this genus. 



The name Lept^enulopsis was proposed by Haupt, in 1878,J but as the work 

 in which it was described has not been accessible, no opinion can be expressed 

 in regard to its value. The term has been used by Jaekel,§ who refers to the 

 species Leptcznulopsis simplex, Haupt, certain small, smooth, semicircular, slightly 

 convex shells, of the age of tfie Wenlock shale. This author also observes 

 that Haupt included in this genus a few shells having the general aspect of 

 Chonefes minima, Sowerby ; but this, according to Dav[DSon, is a strongly plicated 

 shell, though without evidence of cardinal spines. 



* Palsozoic Fossils, vol. i, p. 73, fig. 67 c. 



t See Supiiloment to British Silui-iim Bi-achiopoila, p. 171, pi. xii, tigs. 26-29. 1883. 



* Die Fauna dos Graptolithen-Gesteines; Ein Beitrag zni- Kenntniss der .silnrisi-hen Sediiuentar 

 GesdiiiOie der uoi-ddeutsc.hen El)eiie, vim Karl Haupt. Band liv des Neiien LausitziscOien Magazius, 

 Goi-litz, 1878, p. 31. 



t Deber das Alter des sogen. Graptolithen-Gesteine.'? mit besonderer Bevlicksichtigung der in denselbeu 

 enthaltenen Graptolithen : Zeilschrift dry dcutsi-hen geolngisclien Gesellschaft, vol. xli, p. 69,'). 1890. 



