174 The Molluscan Family Planorbidae 



always directed upward, an upper palatal above and smaller than the lower 

 palatal (2), also pointed upward, and a suprapalatal (1) which is usually 

 in a transverse position. This lamella may be vestigial or absent in some 

 forms of Planorbula. Only one set of lamellae occurs in each shell although 

 the lamellae are found at a very early period in the age of the individual, 

 the old set appearing to be absorbed before the new one is formed as the 

 shell increases through growth. 



Animal (plate 70, fig. 11). The living animal of Planorbula jenksii from 

 Lake Wentworth, New Hampshire, is almost black, the foot with lighter 

 edges. The tentacles are long and tapering, blackish in color with a light 

 zone near the head; a blackish band borders the head and neck above the 

 foot and velar area; the top of the head is wine-colored or reddish, the sides 

 of the body lighter; the black eyes are placed at the inner bases of the 

 tentacles. The mantle is blotched with dark gray dots. The stomach 

 region is pigmented. The liver and ovotestis are yellowish. The velar area 

 is very wide and extends beyond the foot when the animal is in motion. 

 The shell is carried tilted to the left, at an angle of about forty-five 

 degrees. It is sometimes carried flat, the left side lowermost. 



ANATOMICAL CHARACTERISTICS 

 PLATE 37 (Planorbula nnnigcra (Say) ) 



GENITALIA. Male Organs (fig. 4). The seminal vesicle (SV) is about 

 1 nnn. long and 0.5 mm. wide and is composed of a cluster of small glands 

 or follicles. The sperm duct (SPD) is roundly enlarged at its distal end 

 (about 0.5 mm. long and wide) tapering anteriorly to less than half this 

 diameter under the prostate. The prostate (PRS) is about 1.5 nnn. in 

 length and less than 0.5 mm. in height. In section (figs. 1, 2), the prostate 

 is seen to be composed of a long diverticulum to which are attached, on one 

 side only, five or six smaller and shorter diverticula, several of which may 

 be branched two to four times. There are about thirty rows of diverticula in 

 the i:)rostate. The vas deferens is of smaller diameter than the sperm duct, 

 for the most part about half this diameter, and is 6 nnn. long. 



The penial complex (fig. 9) has a strikingly jiyriform preputium, nar- 

 rowing anteriorly to a round tube of small diameter. The preputium is 

 less than 1 mm. long and a trifle more than 0.5 mm. in diameter at its 

 greatest width. The vergic sac is cylindrical in form, about 0.3 mm. in 

 diameter and as long as the preputium. There is only a slight constriction 

 between the preputium and the vergic sac. There is one heavy retractor 

 muscle (RM) attached to the summit of the preputium near the vergic 

 sac. Three wide supporting muscles are attached to the upper and middle 

 area of the preputium. There is no external penial gland duct. The penial 

 complex of another six^cimen shows a more swollen preputium and a wider 

 vergic sac (fig. 10). 



Internally (fig. 11), the preputium has two heavy vertical pilasters 

 (PL) the left one sending a transverse, thick, rounded fold or ridge across 

 the upper part of the preputial sac to the right pilaster. There is a rounded, 

 basin-shaped penial gland (GL), with a shallow cup, the walls of which 

 have many vertical folds (fig. 6, GF). There is no external gland duct, 

 but a shallow channel, open above (DC), connects the penial gland with 

 a circular space bordering externally the high, thick, fleshy muscular ring 

 or diaphragm between the ring and the body wall of the prei)utium 



