140 THE NAUTILUS. 



than any other Pacliychihts I have seen, one with a greatest diam- 

 eter of 24 mm., measuring 39 mm. in height, and having less than 

 two whorls remaining, the suture describing only one spiral turn. 

 The shells from Morelet's collection before me are much smaller, 

 though doubtless this exact form. 



Unio Rovirosai Pilsbry. Laguna de Atasta, near San Juan Bau- 

 tista. See below. 



Descriptions of New Species. 

 Chondropoma Martensianum n. sp. 



Shell perforate, turreted, truncate, thin, corneous, with many faint 

 reddish-brown narrow spiral bands interrupted into dots. 4-| to 5^ 

 whorls remaining in adults, very convex, separated by very deeply 

 impressed sutures, the last whorl well rounded below. Sculpture of 

 numerous very low spiral cords, a median one often larger, giving 

 the upper whorls a subangular appearance, crossed by very numer- 

 ous vertical lamella? with .scalloped edges, about 4 or o lamella? in 

 the space of a millimeter, on the latter half of the last whorl. Aper- 

 ture circular ; peristome broadly and equally reflexed on the outer, 

 basal and columella!- margins, its face somewhat lamellose, nearly 1 

 mm. wide. 



Alt. 13, diam. 6.6, internal diam. of aperture 3.2 mm. (5| 

 whorls.) 



Alt. 11.3, diam. G.5, internal diam. of aperture, 3.3 mm. (4^ 

 whorls.) 



Montaiias de Poana, Tabasco, Mexico (Jose N. Rovirosa). 



This species is most nearly allied to C. radiosum Morelet, but 

 differs as follows : It is smaller and more slender ; the lamellse are 

 not produced into short spines where they cross the spiral cords ; the 

 peristome is decidedly narrower, recurved instead of flat or flaring for- 

 ward ; finally, the aperture itself is as large as in C. radiosum, though 

 the shell is smaller. 



It is named in honor of Dr. E. von Martens, who is now publish- 

 ing an extensive work on the non-marine mollusks of Mexico. 



Unio (Lampsilis) Rovirosai ". sp. 



Shell large, ovate, rather thin (about as in U. luteolus), inflated, 

 nowhere gaping, covered with a rather thin black cuticle, sculptured 

 with coarse and irregular growth-wrinkles, lamellose toward the basal 

 margin; beaks rather small, situated a little behind the anterior 



