THE REPTILES OF THE GALAPAGOS ISLANDS. 79 



or quite disappears between the hips, and on the males it 

 attains a greater development. Each of the large spines 

 of the neck has a small one immediately in front of it, and 

 frequently the latter is preceded by a still smaller one. 

 While young the spines arc subpyramidal, convex on the 

 sides and concave behind, but as they grow higher they be- 

 come more subconical. Early in life the growth is rapid 

 and steady ; later it takes on a periodicity that is plainly 

 indicated in the dorsal spines. Those on the Barrington 

 specimens are encircled by three to six ridges, like the 

 rings around a cow's horn. These make the outward ap- 

 pearance of each spine resemble that of the rattle of a small 

 rattlesnake. In a longitudinal section, however, the layers 

 of the epiderm are seen to lie closely, against each other, 

 not loosely as in the rattle. When with age the shape of 

 the spine becomes subconical, a slight constriction around 

 the base of the cap, or slough, prevents its removal. The 

 periodic growth of the skin lengthens the spine thus push- 

 ing the older cap farther out so as to expose a portion of 

 the base of the new one formed within it. The entire 

 spine being derrral there is no vacant space within the suc- 

 cessive caps, consequently, close as the external resem- 

 blance is, they do not assume the function of rattles. The 

 appearance is brought about by the shape of the cap, or 

 slough, and the periodicity of the growth. Though not 

 a rattle it confirms my account of the structure and devel- 

 opment of that organ as given in 1888 (Bull. Mus. Comp. 

 Zool., xin, 259). Retention of the several caps adds to 

 the firmness and rigidity of the spine. On one individual 

 the longest spines measure three quarters of an inch. 



AMBLYRHYNCHUS CKISTATUS Bell. 



Dr. Baur's Collection contains specimens from Albe- 

 marle, Bindloe, Charles and Tower, and in this museum 



