﻿176 I.AMl'SII.IS 



compressed pseiulocardinals, the anterior the higlier, and two 

 remote laterals ; right valve with one pseudocardinal, a ves- 

 tigial one above it, and one granular lateral ; beak cavities deep 

 with an irregular, double row of dorsal pits ; anterior scars 

 moderately impressed ; posterior scars shallow, large ; nacre 

 white or pale purplish, thicker in front. The male shell is 

 somewhat rhomboid, the posterior termination being widely 

 rounded and below the median line ; the female shell has a 

 small marsupial swelling at some distance in front of the pos- 

 terior end ; the posterior termination is nearly midway up from 

 the base. 



Length 112, height 70, diam. 45 mm. 



Central America ; Tabasco, Mexico. 

 Unio explicatiis Morelet, Test. Noviss, Pt. i, 1849, P- 28. — 



Fischer and Crosse, Miss. Sci., Pt. 7, II, 1894, p. 594, pi. 



LXI, fig. I. 

 Lampsilis exf'licatus Simpson, Syn., 1900, p. 571. 

 Margaron (Unio) semigranosus Lea, Syn., 1870, p. 34. 



A fine series of this species has been lately received by the 

 National Museum from Tabasco, Mexico, collected by Messrs. 

 Nelson and Goldman. 



Lampsilis sapperi von Ihering. 



"This is the shell mentioned by Simpson in his Catalogue, 

 p. 571, n. 4, as a doubtful variety of L. explicatiis. The shell 

 is more elongate, with the ventral margins sinuate and the an- 

 terior extremity lower and somewhat obliquely truncate on the 

 inferior part of the anterior margins. The pseudocardinals 

 are very stout, one in the right, two in the left valve. This 

 differs remarkably from L. explicatiis as figured by Crosse and 

 Fischer, pi. 61, fig. i, of the Moll. Mex., having the pseudocar- 

 dinals elevated, compressed, lamelliform. I believe the L. sap- 

 peri more allied to L. nmhrosiis Lea than to explicatiis, l>eing. 

 however, of a more elongate form with produced posterior 

 extremity and larger size. The type example has a length of 

 64 mm., breadth of 1 14 mm., diam. of 38 mm. The epidemiis 

 IS dark brown, blackish, the nacre white. The posterior slope 



