Subjmnilies, Genera, and Subgenera — Recent and Fossil 121 



ditional si)ecies, recent or fossil, may be found somewhere between these 

 extreme points. At present there seems no alternative but to include the 

 Oregon fossils in Platytaphiiis, since no diagnosis could be made that 

 would include the one and exclude the other. The two species of fossils 

 from Oregon are Platytaphius vialheurcnHiH and P. 7nilleri Henderson and 

 Rodeck, figured on j:)late 37 of the publication cited, figs. 6, a, b, c and 

 9, a, b, c. 



Genus ACRORBIS Odhner, 1937 



Type by original designation Acrorbis petricola Odhner 



1937. Acrorbis Odhner, Archiv. fiir Zoologi, Band 29B, No. 14, ]). 1. Nov. 9, 1937. 



Type Acrorbis petricola Odhner. As genus. 



1938. Acrorbis Pilsbry, Nautilus, LI, p. 107 (review). 



Shell (plate 72, figs. 1-3). Ultradextral, very small, thin, but firm, of 

 circular form, with elevated spire, shell covered with a shining cuticle, 

 openly umbilicatc; whorls slowly increasing, arched, high, simple; aperture 

 very oblique, broadly ovate; lips simple, very thin because of the lack 

 of lime in the mouth-building; shell brown, dark and reddish above, under- 

 side more grayish; apex deep brown, globular, smooth, the following whorls 

 with very weak spiral lines. Height of aperture same as height of whorl. 

 Height 1.5 mm.; diameter 2 mm. (translated from Odhner). 



Animal (plate 72, figs. 5, 6). Gray, the upper surface of the mantle 

 flecked with black. The head is darker gray and neck blackish. The foot is 

 broadly o\'al with thin borders and without any furrows on the sides. The 

 tentacles are narrow, when fully extended, on the end obliciuely truncated. 

 The eyes are on the inner side of the base of the tentacles. The left tentacle 

 differs from the right tentacle in being bifid at the end. The head is 

 sharply pigmented between the eyes. 



ANATOMICAL CHARACTERISTICS 

 PLATE 72 



GENITALIA. Male Organs (fig. 10). No seminal vesicle is show^n in 

 the figure or mentioned in the description. The prostate is almost as long 

 as the uterus and oviduct and has eight large diverticula in a single series. 

 Neither description nor figure indicates the presence of a separate prostate 

 duct. The vas deferens (v) is a long and narrow tube. The penial complex 

 (fig. 9) is elongated, the preputium, about one-third of the entire length, 

 merging into the vergic sac without marked constriction between these 

 sacs. There is a wide retractor muscle (rp) which appears to be attached 

 about midway of the length of the vergic sac. Above the vergic sac there is 

 a wide flagellum less than half as long as the vergic sac. Internally there 

 is a long, tube-like verge and a diaphragm of fleshy ridge separating the 

 preputium from the vergic sac. The upper end of the flagellum is said to 

 liave two cavities, one on each side of a central tube (fig. 9, a). 



Female Organs (fig. 10). The spermatheca (b) is large and globular 

 and is attached to the short, narrow vagina by a very short duct about 

 one-third the length of the diameter of the spermatheca. The uterus (u) is 

 at first as narrow as the vagina, but swells to several times this diameter 

 posteriorly where it joins the nidamental gland. The oviduct is not shown 

 clearly but evidently narrows to the point of junction with the ovisperm 

 duct. The albumen gland is not figured. 



