MUSEUM OF COMPAKATIVE ZOOLOGY. 411 



Patella they had been by distinguished naturalists referred to the generative 

 apparatus. While showing this relation to be improbable, the spongy nature 

 of the organ in some species led me to the suggestion that they might be of the 

 nature of aquiferous pores. It was not until attention was called to them 

 by the investigations of Spengel that their true nature was recognized. 



Super-Family PROTEOBRANCHIA. 

 Family ACM^EID^E. 



Genus PECTINODONTA Dall. 



Pectinodonta Dall, Proc. U. S. Nat. Mus. 1881, p. 409, 1882. 



Shell resembling Scutellina, but with a blunt subcentral apex. Soft parts 

 resembling Acmcea except in the following details. Animal blind, with the 

 front part of the head between the tentacles and above the muzzle much pro- 

 duced upward and forward, extending considerably farther forward than the 

 end of the muzzle, which is marginated with lappets at the outer corners. Jaw 

 thin translucent. Gill exactly as in Acmcea; sides of foot and mantle edge 

 simple, nearly smooth. Dental formula ° ; teeth large, with transverse 



pectinated or denticulated cusps, the serrated edge of which is turned toward 

 the median line. The number of teeth is the smallest in any known limpet, 

 and their appearance suggests that they are compounded of the normal three 

 Docoglossal laterals, rather than due to the suppression of two and the exag- 

 geration of the third. Nothing like it is described in the group. 



Pectinodonta arcuata Dall. 



Plate XXV. Figs. 3,3 a, 3 b. 



P. arcuata Dall, he. cit., p. 409, 1882. 



This was obtained by the party on the Blake at Station 215, off St. Lucia, in 

 226 fms., coarse sand and broken shells, bottom temperature 51°.0; a large 

 dead specimen at Station 185, in 333 fms., fine sand and dark brown mud, 

 off Dominica, bottom temperature 44°.0; another, drilled, but in fresh con- 

 dition at Station 161, in 583 fins., lava sand, off Guadelupe, bottom tempera- 

 ture 41°. 0; another specimen was found entangled in a piece of- coral from 

 unknown depth, at St. Thomas, W. I. 



The typical species was kindly compared with the species of Scutellina in 

 the British Museum by friends in London, and reported to be different from 

 any of them. 



