Sub fcun Hies, Genera, and Suhijeuera- -Recent and Fossil 81 



Animal. When in locomotion the foot is rather long and narrow, 

 rounded before and tapering to a point behind. The tentacles are very long 

 and filiform and the eyes are large, black, and conspicuously placed at the 

 inner base of the tentacles (plate 78, figs. 3, 4). The velar area is well 

 developed. When at rest (plate 70, fig. 4, Tropicorhu havanensis) the foot 

 may be hunched up, rounded, and even the tentacles may be drawn back- 

 ward. The Tropicorbis group is noteworthy for the peculiar pigmentation 

 observed in some species, this consisting of dark, blackish or brownish, 

 markings which show plainly through the shell (plate 78, figs. 3, 4, Tropi- 

 corbis nigrilabris (Lutz) ), and are particularly plain when the animal is 

 removed from the shell (plate 12, fig. 5, T. havanensis (Pfr. ) ). These some- 

 times show on the base, through the shell, as dot-like markings (plate 70, 

 fig. 4, T. havanensis). 



ANATOMICAL CHARACTERISTICS 

 PLATE 12 (Tropicorbis havanensis) 



GENITALIA. Male Organs (fig. 11) . Seminal vesicle (SV) of greater 

 diameter than the ovisperm duct. It is beset with numerous protuberances 

 or glands many of which have the form of club-shaped diverticula. They 

 vary in size anteriorly, the larger vesicles being nearer the ovotestis. The 

 whole seminal vesicle is about 2 mm. long. The sperm duct is over 5 mm. 

 long and is very narrow. It is peculiarly enlarged at the junction of the 

 oviduct and sperm canal and might be considered a carrefour, but that 

 feature is attached to the female system and is a small swelling into which 

 the albumen duct enters (fig. 11, CF). See figs. 7, 8, CF. 



The I'jrostate (PRS) is very long (3.5 mm.) and bears about fifty short, 

 sac-like diverticula. These are placed on a separate duct, the prostate duct, 

 the free portion of which is very short and ciuickly joins the vas deferens. 

 A cross section through the prostate (fig. 9, PD, SPD) shows the relation- 

 ship between these two separate ducts. The vas deferens (VD) is moder- 

 ately long (3.5 mm.) and is a small tube throughout its length except that 

 it is slightly enlarged where it enters the vergic sac (fig. 1, VD). 



The penial complex (fig. 11) is much elongated; the preputium (PR) 

 is cylindrical and slightly longer than the vergic sac ( VS) . In another 

 specimen (fig. 10) the preputium and vergic sac were more nearly equal in 

 length and the upper part of the vergic sac was slightly enlarged. The vergic 

 sac is always of less diameter than the preputium. The retractor muscles 

 (RIVI) are somewhat complicated, there being three branches all con- 

 nected by cross muscles. There are also several small muscles below the 

 retractor muscles which are attached to the mantle and not to the colu- 

 mella muscle. These may be what we have called supporting muscles. There 

 are several series of muscles on the opposite side of the penial complex 

 which we have called supporting muscles (SM). These are attached to 

 the upper j^art of the neck. The upper set, which have small branches, may 

 also help in retracting the penial complex following coitus. 



Internally (fig. 1) the preputium has two or more pilasters. There is a 

 heavy muscular ring or diaphragm which separates the preputial cavity 

 from the vergic space (fig. 1, D, fig. 2). This apparently takes the place 

 of the papilla in Gyraidiis, but there is no second ring below this ring, as 

 there is in Gyraulus. The verge (V), very long and cylindrical, ends in a 



