DALL: MOLLUSCA AND BRACHIOPODA. 283 
to the same species, but pending further investigations I gave it in my notes the 
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. 
The following notes were made upon the animal! (see plate 12, figures 1, 
13, 1e.). The 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. tridentata (= 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 diserimination of species from 
the life is treated with so little consideration by the histologists of to-day. : 
Pelsencer 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 him 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 animal about to be described. - 
The animal swims on its back, the ventral surface of the parapodia uppermost, 
advancing by a jerking motion due to the simultaneous flapping of the parapodia 
at the average rate of eighty strokes to the minute. 
When weary, the animal contracts the parapodia, whieh are then turned back- 
ward, partially overlapping each other and folded fan-wise before being with- 
drawn into the shell (see fi gure 14). When fully expanded, the parapodia in the 
1 U. S. N. Mus. 110,501. 
