BALL: MOLLUSCA AND BRACHIOPODA. 233 



to the same species, but pending further investigations I gave it in my notes tlie 

 varietal name of C occidentalis ; the large Atlantic form, or anything correspond- 

 ing to the Mediterranean animal not having been obtained in the Northeast 

 Pacific during fifteen years of collecting. 



Tlie following notes were made upon the animal ^ (see plate 12, figures 1, 

 1^, 1^.)- Tlie fully adult shell measures 9 mm. long, 6 mm. in greatest width, 

 and 5 mm. in greatest convexity. The " appareil de fermature " consists of 

 a tooth-like process projecting on each side from the ventral plate and entering 

 a depression in the inner side of the dorsal plate. The ventral lip is strongly 

 constricted close to its narrowly reflected anterior margin. The posterior median 

 spine is usually decollate at the tip. The back has a broad median and two 

 narrower lateral obscure ridges ending at the thickened "bridle" or concentric 

 callous ridge characteristic of this species ; the ventral plate is most convex in 

 front, where it is suddenly constricted ; the portion near the aperture strongly 

 marked by concentric whitish impressed lines with wider interspaces, though these 

 do not interrupt the smoothness of the surface. The " hood " or produced margin 

 of the dorsal plate, instead of being produced in a nearly continuous plate as 

 figured by Boas for C tridenlata {= telemus), is bent ventrally in a curved 

 manner over the aperture, and about half the anterior convexity of the ventral 

 plate is thus overshadowed. The whole shell is shorter and more globose than 

 the Mediterranean form as figured by Boas, and the lateral slits behind the inter- 

 locking processes form a straight even line, not arcuate and anteriorly expanding, 

 as in the figures referred to. 



It seems amazing that, with the opportunity at Naples and elsewhere, neither 

 the author of the " Challenger " Report, Boas, nor any other recent writer on these 

 animals, has troubled himself to give a drawing from life of the animal forming 

 the type of the genus, nor even a careful description of its external characters 

 while living. So we are obliged to fall back on the drawings and engravings of 

 the field naturalists of half a century ago, whose discrimination of species from 

 the life is treated with so little consideration by the histologists of to-day. 



Pelseneer has given us an excellent generalized description of the anatomy in his 

 "Challenger" Report, comparing it with the more archaic Cleodora. But no 

 attempt is made by liim to compare all the anatomical features of the several 

 species among themselves in this genus. Any one, however, who compares the 

 best existing figures of the living animal, such as those in the voyage of the 

 " Bonite," will be struck by the extreme differences between any one of them 

 and the anmial about to be described. 



The animal swims on its back, the ventral surface of the pampodia uppermost, 

 advancing by a jerking motion due to the simultaneous Happing of tlie parapodia 

 at tlie average rate of eighty strokes to the minute. 



When weary, the animal contracts the parapodia, which are then turned back- 

 ward, partially overlapping each other and folded fan-wise before being with- 

 drawn into the shell (see figure \b). When fully expanded, the parapodia in the 



1 U. S. N. Mas. 110,501. 



