﻿284 NM I'lIKON'AIAS 



1 have never seen the type of this species nor anythinc^ more 

 than a sin^^le valve of what is proljably an antlientic specimen, 

 but if Fischer and Crosse's fig^nres are correct I am a little 

 doubtful whether it can eipial Sowerby's Unio zrllicatiis, as 

 von Martens believes. The National ATuseum possesses spec- 

 imens, which ai^ree almost absolutch' with tlie ori^s^inal fij^^ure 

 and description of I'cUicatus and it is a peculiar species. More- 

 let's species seems to be solider and more decidedly biangulate 

 behinfl, yet the two forms may run tog^ether. \'on Martens 

 figures a young female shell with rays. \ on Martens makes 

 the Unio rcrcc-paci.^ of Tristram a variety of the above, and fig- 

 ures it. His figure certainly is the same as that of the Unio 

 7'cHicatits Reeve in the Conchologia. Tristram's description 

 does not seem to me to agree with this, as he says his shell has 

 a shining purple nacre, while that of 7'ellicata is dull lurid and 

 ashy-brown. 



Yar. tnajitscitht (von Martens). 



"Of larger size ; the summits somewhat more advanced. 



Long. 5Q, alt. vert. 2y, ala 28, diam. 17.5 mm. 



Long. 58, alt. vert. 26, al?e 2y, diam. 17.5 mm. 



Long. 55, alt. vert. 26, ahe 27, diam. 20 mm. Vertices in 2/7 

 long." (von Martens.) 



Type locality. Lake of Yzabal, E. Guatemala. 

 Unio raT-istcIlus var. majuscuhis von M.artens, Biol. Cent. 



Amer.. Moll., tqoo. p. 516. 



"The dimensions given above show that this form varies 

 considerably in the general outlines." 



Nephron.mas \'fjj.icata (Reeve). 



Shell rather small, long elliptical or long rhomboid, sub- 

 solid, somewhat convex. ine(|uilateral. with a well-developed, 

 generally double, posterior ridge : beaks moderately full, their 

 sculpture not seen; surface delicately concentrically ridged; 

 epidermis smoky-brown, rayless in adult specimens; left valve 

 with two subcompressed pseudocardinals anrl two curved lat- 

 erals ; right valve Avith one pseudocardinal. often with a second 



