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 ai'e hidden (ahp), Plates XII. and XIX. 



TJie 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 

 (rpoVcajs, 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 Gamaan, 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, Dec. 12, p. 524. 



Didijnwdus 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 sharlrof 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 



