THE COOK'S OR HARVEY ISLANDS. 391 



peristome thin, simple, straight; parietal region with one or two, and the palate 

 with (rarely without) two or three internal laminae; columella emarginate and 

 furnished with a spiral fold. 



Animal small; eye peduncles long and slender; tentacles small; foot short, 

 narrow, pointed behind. 



"Teeth (i. tumuloides) 17-1-17, with about seven perfect laterals. The base 

 of attachment of the centrals is subequilateral. There are distinct side cutting 

 points and cusps. The median cusp is long. Laterals unsymmetrical as usual. 

 Transition formed as usual. Marginals low, wide, with one long, large, bifid inner 

 cutting point and one small side cutting point." (Binney.) 



Remarkable for their singular habit of ovopositing into their cavernous um- 

 bilicus. The eggs usually from four to six, or the same number of very young 

 shells may frequently be seen closely packed in the cavity. The latter are shaped 

 almost exactly like a half-grown Planorbis trivolvis. The first whorl is smooth, 

 the second one with radiating costulate striae, and the internal laminae both on the 

 penultimate and second whorl can be distinctly seen through the transparent shell. 



The peculiar constriction of the umbilicus does not occur until the last two 

 whorls are completed, previous to which it is very open or cup-shaped. 



Certain species more completely secure the safety of the eggs by the formation 

 of a very thin shelly plate which projects from the columellar and parietal region, 

 and nearly closes the umbilical opening. It is subsequently either broken away 

 or absorbed by the animal to facilitate the escape of the young shells. 



All the species, which are gregarious, live under loose stones, rotten wood, and 

 less frequently buried in decaying leaves. They range from the low lands near 

 the sea-shore to upward of two thousand or more feet above sea-level. 



So far as known, the genus, which comprises about a dozen species, is peculiar 

 to the Society and Cook's Islands. In the former group they are confined to 

 Tahiti and Moorea. Dr. Pfeifi"er mentions the Marquesas as the habitat of 

 Jacquinoti, which is undoubtedly an error. I searched every island, except one, in 

 that group and did not find a single specimen. Mr. Pease, who received large 

 numbers of small land shells from that group, also failed to get specimens, and 

 shared my doubts in regard to its occurrence there. 



The latter author classed them with Pitf/s. Albers and Peetel referred them 

 to Endodonta, and Schmeltz to Patula. They are more nearly related to Endo- 

 donta than to either Piti/s or Patula ; but the peculiar formation of the umbilicus 

 Avill readily distinguish them from any of the above genera. 



