35 



ficient to Mr. Davidson to authorize its separation from 

 IStropJiomena (1853, p. 108), and thus retain the name Leptaena, 

 which had been so widely used in paleontological literature. 

 This specie^thus became the type of the restricted genus, 

 and the latter has very generally been adopted. 



In 1830, however, Pander described his genus Plectam- 

 ho7iites, in which he placed a number of species, the whole 

 forming an assemblage apparently about equivalent to Lep- 

 taena or Stropliomena, as these terms were used in their un- 

 restricted sense by early writers. The interior of some of 

 his species is unknown, including the first species, and 

 there are probably both Leptaenas and Strophomenas (as 

 restricted) contained in the genus. But his first of two 

 generic figures appears to be the dorsal valve of a species 

 of Stropliomena of the rhomhoidalis type, while his P. tri- 

 angularis, imbrex, and another (all vars. of one sp.), which 

 have been examined and figured by Mr. Davidson, have the 

 dorsal valve concave, as in rhomhoidalis. Should therefore 

 it be necessary (as seems improbable) to separate the genus 

 Strojjhomena as understood by Davidson into two groups, 

 respectively typified by rJiomhoidalis and rugosa [planum- 

 hona). Pander's name might be utilized for the former, 

 although M'Coy has (1844) also suggested a name [Lepta- 

 gonia) for this identical group. 



Stropheodonta of Hall (1850, Pal. N. Y. ii) seems tolerably 

 distinct from the above, if the total absence of any indica- 

 tion of a covered or open foramen, which is said to charac- 

 terize it, be confirmed. 



A different arrangement from that adopted by Davidson 

 was proposed by Professor King, by which S. rhomhoidalis 

 was to represent Lcptaena, and L. transversalis and congeners 

 would be the exemplars of Plectamhonites. Whatever may 

 have been the points in favor of this arrangement, it may 

 be said that no part of it was imperatively required by the 

 rules of nomenclature, and, as another grouping has come 

 into general use, which is at least equally conformable to 

 those rules, it would be highly undesirable to inaugurate 

 any further or unnecessary changes. 



Orthotheies of Evans (1837, q. v.) is also a synonym of 



