178 The Molluscan Family Planorbidae 



Genus PROMENETUS F. C. Baker, 1935 



Type by original designation Planorbis exacuous Say 



1928. Menetus F. C. Baker, Fresh-water Moll. Wis., I, pp. 357, 360, 362 (non H. and 



A. Adams). Genitalia of Planorbis exacuous Say 

 1935. Promenetus F. C. B.\ker, Nautilus, XLIX, p. 48. Type Planorbis exacuous Say. 



As new group 



Shell (plate 79, figs. 19-21). Ultradextral Avith a small number of whorls 

 rapidly increasing in diameter, carinated or rounded; left side with broad 

 spire depression exhibiting all of the whorls; right side flat, also exhibit- 

 ing all of the whorls; aperture wider than high; outer lip thin. 



Animal. External features similar to those of Planorbula. Foot very 

 short and rounded. Color blackish. 



ANATOMICAL CHARACTERISTICS 

 PLATE 41 {Promenetus exacuous (Say) ) 



GENITALIA. Male Organs (fig. 10). The seminal vesicle (SV) is about 

 2 mm. long, is nearly three times the diameter of the ovisperm duct and has 

 many small diverticula or vesicles, about as long as the diameter of the 

 seminal vesicle, projecting from one side of the organ. The sperm duct 

 (SPD) is about 1.5 mm. long and 0.3 mm. in diameter and appears 

 sausage-shaped. The prostate (PRS) is 1.5 mm. long and is composed of 

 thirteen multiple diverticula. In section (fig. 5) the prostate is seen to have 

 four supplementary diverticula projecting from the side which lies next 

 to the oviduct. An unusual form of prostate is shown in fig. 11, plate 42 

 (P. exacuous megas) in which the three supplementary diverticula are each 

 branched three times at the extremity. The vas deferens (VD) is about 7 

 mm. long and about one third the diameter of the sperm duct, which, itself, 

 also diminishes greatly in diameter beneath the prostate. 



The i)enial complex (plate 41, fig. 2) is 3 mm. long, the pyriform 

 preputium occupying half of the length, the much narrower vergic sac the 

 other half. There is no sharp constriction between the upper and lower 

 sacs, the preputium simply narrowing as it joins the vergic sac. There is 

 one narrow retractor muscle (R]M) and a wide group of three to five 

 sujiporting muscles (SAI) forming a lattice-like pattern. The vas deferens 

 enlarges only slightly as it enters the vergic sac (VD). In fig. 1, a penial 

 complex is shown in which the preputium is much swollen by the enlarged 

 penial gland. The penial complex of variety mcgas docs not differ from 

 that of exacuous. 



Internally (fig. 3), the preputium has two heavy pilasters (PL) to the 

 upper part of the left one of which the penial gland is attached (GL). The 

 gland appears sac-like as seen from the side and is bent crosswise in the 

 cavity of the preputium. There is a wide projection at the end of the gland 

 in which there is an open groove (DC) or channel connecting the gland 

 with the muscular ring or diaphragm (D) and separating the upper from 

 the lower cavity. In fig. 3 on plate 42, the penial gland is shown from 

 above, the pilasters separated to show the ovate cup of the gland and the 

 glandular folds lining the walls of the cup. A longitudinal section of the 

 gland (plate 42, fig. 7) shows the arrangement of the vertical folds within 

 the gland. 



The verge (V) is long and narrow, usually filling the vergic sac (plate 

 41, fig. 3) and protruding from the diaphragm into the preputial cavity. 



