24 ENDODONTA. 



the shell seen from above. The half grown shells are widely umbil- 



/ 



icated, and resemble the normal Endodontas in form and teeth. 



This group also has descended from the Endodonta stock, being 

 differentiated only by the constriction of the mouth of the umbilicus. 



Garrett writes as follows . " Remarkable for their singular habit 

 of ovipositing into the cavernous umbilicus. The eggs usually from 

 four to six, or the same number of young shells, may frequently be 

 seen closely packed in the cavity. 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 their 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 sub- 

 sequently either broken away or absorbed by the animal to facilitate 

 the escape of the young shells. All the species are gregarious, liv- 

 ing under loose stones, rotten wood, and less frequently buried in 

 decaying leaves. They range from the low lands near the sea-shore 

 to upwards of two thousand 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 con- 

 fined to Tahiti and Moorea." 



E. cavernula H. & J. iii, 69. E. coarctata Pfr. iii, 71. 



E. sculptilis Pse. iii, 70. ttrrricula H. & J. 



fratercula Pse. streptaxon Rv. 



E. subcavernula Tryon, iii, 70. E. bursatella Old. iii, 71. 



cavernula Garr. not H. & J. E. retunsa Pse. iii, 71. 



E. tumuloides Garr. iii, 70. E. heynemanniPfr. iii, 72. 



E. jacquinoti Pfr. iii, 71. E. gregaria Garr. iii, 72. 



excavata H. & J. E. recedens Garr. iii, 72. 



Subgenus ENDODONTA Albers. 



Shell more or less depressed, varying from rounded to acutely 

 keeled at the periphery, umbilicus generally open, rarely minute or 

 closed, and never contracted at its opening. Aperture armed within, 

 with teeth or entering plates (rarely absent by degeneration). 



This group comprises a great number of species, and is especially 

 characteristic of the Polynesian fauna, although a few forms are 

 found as far to the west as New Zealand, New Caledonia and the 

 Philippine Islands. The species are unequally related, as is usually 

 the case in large groups ; and several minor divisions (Thaumato- 



