MUSEUM OF COMPARATIVE ZOOLOGY. | 21 
men there is no appearance of a urethral papilla; the anterior border of 
the opening is inflated into a flap or valve, which closes the opening 
against objects passing outward through the cloaca, or, better, which is 
made to close it by the objects themselves. The mouth of each of the 
abdominal pores is inflated in a similar manner into a broader flap, by 
which the pores are hidden (abp), Plates XII. and XIX. 
The Abdominal Folds. 
Plate XX. Figs. A, B. 
As represented on the plate, section B is of natural size. The folds 
become less prominent near the pectorals and toward the pelvis. The 
section was made eight inches in front of the latter. In each figure 
the inner wall of the belly has been stretched to its utmost, so that 
the prominence of the folds is not overdrawn, As stated above, the 
folds hang three quarters of an inch lower than the skin of the body 
at their outer sides, and are separated below by a groove. One of the 
folds is seen to hang below each of the large abdominal vessels. The 
vessels are parallel or nearly so. Between them there are two mus- 
cular bands, one to each fold. Each band is nearly an inch in width, 
very thin at its lower edge, and near one fifth of an inch thick toward 
the rounded upper edge, between the veins. The fibre in these tropeic 
(tporews, the keel of a ship) or keel muscles differs from that in the 
walls of the flank in being coarser in the bundles and plates, and more 
loosely put together. Apparently the keel muscle corresponds to the 
rectus abdominis of other vertebrates. 
History. 
Chlamydoselachus anguineus Garman, 1884, Jan. 17, Bulletin of the Essex Institute, 
Vol. XVI., —Science, Feb. 1, p. 116, — Science, Mar. 21, p- 345, — Science, Nov. 
28, p. 484; Gill, 1884, Science, Mar. 21, p. 346, — Science, Apr. 11, p. 429, — Sci- 
ence; Deen 120m p24, 
Didymodus anguineus Cope, 1884, Mar. 7, Science, p. 275 (change of name only), — 
American Naturalist, April No., p. 412, — Science, May 30, p- 645, — Pal. Bull., 
No. 38, printed July 1, pp. 572, 588, 589, and Proc. Amer. Phil. Soc., same article. 
The specimen from which the description and figures given below have 
been taken is the only one of this shark of which we have any knowl- 
edge at present. It was purchased in a miscellaneous lot of alcoholic 
Specimens by the Museum from Prof. H. A. Ward, who had secured it 
