252 PROCEEDINGS OF THE ACADEMY OF [1898. 



similarly shaped dark stripe running backward from the mantle, 

 sometimes well-defined, sometimes faint. Mantle buff or red, with 

 two curved lateral black bands (sometimes obsolete) and scattered 

 black maculation or marbling. Shell rectangularly oblong, 2 or 3 

 mm. long. 



Epiphallus slender, long, and tapering dlstally, having an abrupt 

 kink at base, secured by a short muscle, as usual in the genus. 

 Vas deferens neither lengthened nor convoluted. Vagina apparently 

 functional as a penis. Spermatheca globose or oval, on a short, stout 

 duct which is directly continued into the vagina. Free oviduct 

 short and slender. Ovo-testis a rather loose bunch of oval follicles 

 (fig. 38). Albumen gland unusually hard and brittle. The right 

 eye retractor passes between the branches of genitalia. 



In one specimen (PL XII, fig. 37) there seems to be a glandular 

 enlargement of one side of the base of the epiphallus with a small 

 tubercle on the other side. This may be pathologic. 



Jaw (PL XVI, figs. 94-96) arcuate with a slight median projec- 

 tion below, covered with flat, narrow, crowded ribs separated by 

 very narrow, shallow intervals, or with flat, slightly imbricated 

 plaits (or merely densely, irregularly striated vertically in form 

 humile, see above.) 



Radulawith 35-1-35 teeth. Centrals tricuspid ; laterals lacking 

 the entocone ; marginals formed by union of ectocone with mesocone 

 and shortening of the basal-plate. The cusps are short throughout. 

 The change from laterals to marginals is so gradual that it is prac- 

 tically impossible to draw a line between them. On some outer 

 marginals the ectocone is bifid. The figure shows a central with 

 one lateral and a group of three inner marginals. 



Well and constantly distinguished from P. Andersoni and folio- 

 latum externally by the wide, light dorsal area enclosing a darker 

 median stripe, and bounded laterally by blackish bands. Inter- 

 nally, the slender, tapering epiphallus and short vas deferens are 

 even more characteristic. The scarlet color of the back, noticed by 

 Cockerell in some specimens, is not accidental, but of common occur- 

 rence. 



In form the species varies (in alcohol) from a long, vermiform 

 shape to about the contour of P. Andersoni. 



The body-cavity extends nearly to the end of the tail. Self- 

 excision of the tail occurs, but the amputated portion is short, as in 

 P. Andersoni, and the great majority of individuals we have seen 

 show no oblique constriction of the tail. 



