Subfamilies, Genera, and Subgenera — Recent and Fossil 183 



1931. Mcnclus Thiele, Handbuch, p. 481. Type Planorbis opercularis Gould. As sec- 

 tion under Hippeutis, subgenus of Anisus 



1934. Menctus Pilsbry, Proc. Acad. Nat. Sci. Phil., 86, p. 63. Type Planorbis oper- 



cularis Gould. Anatomy. As genus 



1935. Menetus F. C. B.aker, Nautilus, XLIX, p. 47. Type Planorbis opercularis 



Gould. Anatomy. As genus 



Subgenus MENETUS SS. 



T^■])o Phowrbis opercularis Gould 



Shell (plate 79, figs. 22-24). Small, ultradextral, of few rapidly enlarg- 

 ing whorls, the body whorl of large diameter compared wdth the inner 

 whorls; right side flat, left side with the spire whorls deeply immersed; 

 periphery or shoulder of body whorl more or less carinated ; aperture wide, 

 more or less expanded; outer lip usually thin. 



Animal. The foot is comparatively short, the tentacles long and filiform. 

 Color generally blackish. In general features the animal is like that of 

 Planorhula. 



ANATOMICAL CHARACTERISTICS 



PLATES 38 AND 39 



GENITALIA. Male Organs. [Menetus opercularis, type of the genus, 

 plate 38, fig. 1). Seminal vesicle (SV) about 0.5 mm. long, twice the di- 

 ameter of the ovisperm duct and about the same length. The vesicle proper 

 has a few wide lobes, but the lower part (the ovisperm duct) is lined with 

 small vesicles on the side. Sperm duct (SPD) about 1 mm. long, rather 

 thick. Prostate (PRS) about 0.5 mm. long with about a dozen main 

 diverticula. In section (fig. 2), the prostate shows several small diverticula 

 projecting from a single, vertical diverticulum, there being usually five 

 branches, one or more of which may be divided two or three times at the 

 end (as in figs. 2, 3), or all may be single, long and club-shaped, as in 

 cooperi (fig. 14). The vas deferens is 3 mm. long, about half the diameter 

 of the sperm duct, and slightly enlarged as it enters the vergic sac. 



The penial complex (fig. 10) is elongated and sac-like, about 1.5 mm. 

 long, of which the preputium, narrowed at the male genital opening, 

 occupies 1 mm. or two-thirds of its length. There is a slight constriction 

 between the preputium and the vergic sac (VS). There is one narrow re- 

 tractor muscle (RjNI) attached to the base of the vergic sac. There are four 

 sets of supporting muscles (SM) attached to the preputium. Most of these 

 are branched several times. 



Internally (fig. 8), the preputium has two pilasters (PL). At the upper 

 part of the preputium, there is a short penial gland which is doubled over 

 in the normal position (GL). When expanded (fig. 6), this gland is 

 trumpet-shaped, the bell-like cup fiaring. The cup cavity is provided with 

 vertical folds, as in other Planorbidae. There is a dependent ring or dia- 

 phragm between the preputium and the vergic sac cavity (D in fig. 8). The 

 verge (V) is elongated and tapering and normally as long as the vergic sac. 



Female Organs (fig. 1). The spermatheca (S) is ovate, about 0.3 mm. 

 long and has a very narrow duct (SD) almost 1 mm. long, which enters 

 the short and narrow vagina (VG). The uterus (U) is about 0.2 mm. wide 

 and 1 mm. long. The oviduct (CD) is very short (about 0.4 nnn.) and 

 enters the ovisperm duct without notable decrease in size. There is a large 



