226 AMERICAN JOURNAL 



yellowish horn color, tessellated above with chestnut-brown, be- 

 neath radiately striped with the same hue ; spire obtuse, roundly 

 tumulose ; whorls 7, flatly convex, the last one angular, acutely 

 carinate on the periphery, obliquely striated, striae more distant 

 and plicate on the three upper whorls ; suture linear, marginated 

 above with a slight carina ; umbilicus large, profound, cavernous, 

 much constricted ; base flat, convex ; aperture transverse, sub- 

 rhomboidal, fauces with two median approximating lamella ; peri- 

 stome thin, slightly sinuous, continuous with the acute margin of 

 the umbilicus ; columella subvertical, thin, sinuous, with a me- 

 dian obtuse fold, which sometimes is obsolete ; parietal region 

 with a median lamella. 



Height, 4$ mill.; diam., 7 mill. 



Habitat, Rarotonga Id., Cook's Isles. (Coll. Garrett and Phila. 

 Acad.) 



This singular dome-like species we found abundantly in but one 

 location, high up in a mountain ravine. They live under stones 

 and among dead wood and decayed leaves. 



The animal is cinereous, with dusky neck and tentacles. The 

 foot is small, narrow and tapering behind. The upper tentacles 

 are very long, the lower ones very small. It possesses the sin- 

 gular habit of ovipositing into its cavernous umbilicus. In fact, 

 this habit is peculiar to all the species of this type, which com- 

 prises several species, all belonging to the Cook's and Tahiti 

 group of islands. No doubt the sporadic islands south of Tahiti 

 will produce other species. 



The young shells found in the umbilicus are white, hyaline, and 

 shaped like a Planorbis. Even at that early age the lamella in 

 the fauces maybe distinctly traced through the translucent shell. 

 The whorls are distinctly plicatcly striated. 



Helix Jacquinoti, Pfr., H. bursatella, Gld., H. retunsa, Pse., 

 H. fratercula, Pse., are all Marsupial Helices ; the three first 

 inhabit Tahiti, and the last the Cook's Group. 



Pitys Cavernula, Garrett. Plate 19, fig. 16. 



Shell umbilicate, subglobosely conoid, rather thick, cinereous, 

 or brownish-horn color, sometimes deep brown, generally tessel- 

 lated above with the latter color, beneath obscurely rayed ; spire 

 obtuse dome-shaped, some more elevated than others ; whorls 7, 

 convex, last one acutely carinate, finely ribbed, ribs closely set, ob- 

 lique, curved, interstices minutely striated ; base flattened, convex, 

 striated, but not ribbed ; suture corded above with the spiral 

 keel ; umbilicus large, deep, cavernous, contracted at the margin ; 

 aperture transverse, subrhomboidal, fauces with two, rarely three, 



