PLBKOCHS1LU8. XV11 



Genus PLEKOCHEILUS Guilding, 182H. 

 Man. Conch, x, p. 6*2. 



Shell ovate, usually solid and opaque and zigzag-strenkc<l or dap- 

 pled with brown. Aperture large, ovate, the peristome expanded, 

 refiexed or blunt, columella bearing a fold, or simple. 



There are two small, well-separated frontal lobes on the left side 

 of the mantle. Kidney (of P. blainvilleanus} very short, triangular, 

 not projecting beyond the pericardium. 



Genitalia (P. blainvilleanus, pi. 50, fig. 3, after Semper) : Atrium 

 very short ; penis moderately long, continued in a long epiphallus 

 which terminates in the vas deferens and a long flagellum; " retractor 

 muscle inserted about the middle." Vagina short and wide. Sperma- 

 theca globular, on a very long duct, as long as the oviduct. (The 

 penis is shown exserted in the figure). Jaw arcuate, composed of 

 numerous delicate plaits, 41 in P. blainvilleanus (pi. 50, fig. 4. after 

 Schako), about 60 in P. aulacoslylus. 



Radula broad, the rows of teeth widely V shaped (pi. 50, fig. 12, 

 P. blainvilleanus*), composed of 62,1,62 x 110 teeth (blainvilleanus, pi. 

 50, figs. 5, 6). In this species the basal-plates are longer than the 

 cusps ; central tooth with a stout middle cusp, side cusps small ; lat- 

 erals similar but with no inner cusp ; marginals irregularly denticu- 

 late. In P. aurissileni and P. aulacostylus (pi. 50, figs. 9, 10, after 

 Binney) the mesocones are long and acute, reaching beyond the 

 basal-plate; in the former the side-cusps are sub-obsolete, in the latter 

 well developed. 



Type, P. aurissileni (Born). 



Distribution : Northwestern South America, St. Vincent aiid St. 

 Lucia. 



My knowledge of the soft anatomy of this genus is from the work 

 of Semper, Binney and Schako. It agrees in all respects with Bidi- 

 mulus except that Semper states that there is a flagellum on the 

 penis. This seems to me very doubtful. The structure he figures 

 may rather be the retractor muscle of the penis. The rank of Pleko- 

 cheilus as a genus rests upon its conchological peculiarities. 



Section Plekocheilus s. str. 



Man. Conch., x, p. 64. 



Shell wrinkled or malleate, the spire costulate. 



