62 THE NAUTILUS. 



PachycMlus glaphyrus Morelet. 



This species is an exceedingly variable one, more so perhaps than 

 any other Mexican Melanian. The American student, however, 

 will readily call to mind cases of equal variability among the species i 

 of oui' Southern States. The material sent by Prof. Rovirosa com- 

 prises a number of varietal forms not before made known. 

 P. glaphyrus Rovirosai Pils. (PI. I, figs. 9, Id.) 



Shell large and heavy, elevated conical, the lateral outlines 

 straight above, modified by the slight convexity of the whorls below. 

 Spire more or less truncated at tip, half-grown specimens, (PI. I, fig. 

 9,) possessing 8 remaining whorls ; adults, (PI. I, fig. 10,) having one 

 or two whorls less. 



Surface most minutely spirally striated the striae visible only 

 under a lens. Young and half-grown specimens are otherwise 

 smooth, except for very slight spiral lirse toward the base. When 

 a little more than half-grown, there appear coarse, oblique, curved 

 wave-like folds on the body-whorl, extending to the periphery but 

 not below it. Simultaneously with these undulations, begin spiral 

 spaced lirae crossing them, which are slightly more prominent on 

 the crests of the waves. This sculpture continues upon all subse- 

 quent volutions. The last volution of an adult specimen is slightly 

 compressed below the suture, then quite convex. It has ten waves, 

 and about nine spiral lirae, but the number of these last is quite 

 variable on different specimens. 



The color is olive in young, blackish in old examples : interior of 

 the mouth white, maculated with brown at the position of the 

 periphery and folds. This marking is also seen on the eroded spire 

 in some specimens. 



Aperture ovate, acute above, slightly exceeding one-third the 

 total length of the shell. Columella white, regularly arcuate, 

 spreading in a brown-tinted callus. 



Dimensions. An adult specimen measures: Alt. 78, diam. 28 

 mm. Aperture, alt. 25, width 18 mm. A younger specimen 

 measures ; Alt. 56, diam. 20 mm. Aperture, alt. 20, diam. 12? mm. 



Collected from a spring which gushes from the western brow of 

 the little ridge of the Limon, State of Tabasco, Mexico. 



This form is allied to P. glajihyrus typical, and to, the var. scam- 

 nata, but it is distinct from both. The form is notable for its stout, 

 straight-sided sjiire, non-impressed sutures, and the unsculptured 

 young. 



