338 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



or in the sutures. Aperture large, forming more than a half-circle; 

 outer side well rounded, nearly straight on the columella-margin; lip 

 continuous all around, raised up and with the edge slightly everted, in 

 the umbilical region, so as to ])artially conceal the umbilicus, which is 

 rather large and deep, nearly circular. Operculum s^iiral, thin, horny, 

 round-ovate, with the nucleus excentric and with two to three rapidly 

 increasing whorls. 



The animals of several alcoholic sjiecimens were examined. Head 

 large, short, thick, rounded or truncate, with two short, Hat, obtuse 

 anterior tentacles, wide apart, but connected together by a transverse 

 fold; posterior tentacles short, thick, conical, smooth; no eyes visible. 

 Pharynx short, thick, retractile; jaws crescent-shaped, strong, black. 

 Verge situated just below the right posterior tentacle, small, papilli- 

 form, swollen at base; below this and farther back, a larger and thicker 

 l)apilla, with basal swelling ; on each side, between the mantle and foot, 

 at about mid-length of the foot, a small mammiform i)apilla; two small, 

 flat cirri behind and beneath the operculum. Foot broad, ovate, with 

 two tentaculiform i)rocesses in front. 



The largest specimens are badly broken; some of them were about 

 10""" in length; greatest diameter of operculum, 6'""'; its breadth, 4.5"'"'. 

 A perfect, but small, specimen is G""" long; breadth, G"'"'; length of body- 

 whorl, 5.2"'"'; length of aperture, 4"""; its breadth, 3.2""". 



Station 1031, oft" Martha's Vineyard, in 255 fathoms, 1S81. About a 

 dozen specimens, all living, were taken from the interior of an old egg- 

 case of a skate {Raia, sp.). Most of them were badly broken. 



I have comi^ared these specimens directly with original specimens of 

 the fossil Choristes elcgans, found in the post-pliocene of Canada by Prin- 

 cipal J. W. Dawson, who very kindly sent me specimens, both adult and 

 young. 



Our specimens agree very closely with the smaller fossil ones in form 

 and structure. The principal difference is in the much thinner and 

 more fragile texture of the recent shells. This may be due to mere 

 local conditions. Therefore, until more specimens of the recent shells 

 are obtained, I prefer to consider it a thin and delicate A\ariety of the 

 ancient type. 



Koonsia Yerrill. 

 Trans. Conn. Acad., v, p. .545. 



Allied to Fleurohrancluvcij with which it agrees in the character of 

 the head, tentacles, proboscis, and gill. It differs in having the back 

 swollen and overhangiug, both on the sides and posteriorly, with a dis- 

 tinct mantle-edge all around, and with a wide groove between it and the 

 foot posteriorly, as well as laterally ; the foot is narrower and prolonged 

 posteriorly, with a specialized glandular groove near the end, beneath, 

 and a conical papilla above, near the tip. 



The external reproductive organs appear less complicated than in 

 Pleurohrancluva. 



