﻿314 pr.ACioi.A 



surface covered w itli tine, oramilous, concentric ridg^es ; epi- 

 dermis olive or dark olive-brown, havint^ impressed radial 

 lines over its hinder half, between which lines it is often 

 looped ; left valve with two subconipressed, ragged pseudo- 

 cardinals and two laterals, the lower higher ; right valve with 

 one pseudocardinal. a vestigial second one above it, and one 

 lateral ; beak cavities not deep ; muscle scars scarcely im- 

 pressed : nacre dull, lurid or lead-color, frequently blotched. 

 Male shell ovate, pointed behind a little above the base ; female 

 shell almost elliptical, with a decided marsupial swelling, the 

 posterior point blunt and well elevated. 



Length yj, height 28, diam. 20 mm. 



Nicaragua. 

 Un'io (Plagiola?) imbricatiis Morch, Mai. P.latt.. MI, 1860-1, 



p. 205. — Simpson, Syn., 1900, p. 607. 

 Unio imbricatiis von Martens, Biol. Cent. Am., Moll., 1900, 



p. 498, pi. XMii, figs. 6, 6a-c\ 



Unio encarpus Lea, Pr. Ac. N. Sci. Phila., XH, 1868, p. 95 ; 



Jl. Ac. N. Sci. Phila., VI, 1868, p. 294. pi. xui, fig. 105; 



Obs., XII, 1869, p. 54, pi. XLii, fig. 105. 

 Margaron (Unio) encarpus Lea, Syn., 1870, p. 35. 

 Plagiola encarpa Simp.son, Syn., 1900, p. Cyoy. 



Von Martens has figured in the P)iologia Morch's Unio 

 imbricatus and I agree with him that Lea's Utiio encarpus 

 published eight years later is a synonym of the fomier. There 

 is a good deal of variation in the sculpture, some specimens 

 scarcely showing radial grooves, while in others they are very 

 distinct. The type of Unio encarpns is radially grooved. 



Group of Plagiola solid. 



Shell triangular ovate, inflated, solid, with a high, rounded 

 or narrowly subangulate posterior ridge ; beaks full ; epider- 

 mis rough and black ; hinge heavy ; bccik cavities rather deep ; 

 nacre whitish, thicker in front ; female shell with a strong 

 marsupial swelling. 



