258 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



very } oung Callorbynclu, and others of a later period in which tritors, like those 

 of Callorbynchiis suntbii, were present on the sides of the teeth, and yet others, 

 still later, in which by change of feeding habits the impact had been changed 

 to the front edges of the palatine and the mandibular teeth, where the stress 

 or impact is generally exerted, and where tritors now are in all except very 

 early stages of Chimaera. Xo better way at present suggests itself to account 

 for the differences in dental structure found in Chimaera and Callorhynchus. 

 On Plate 7, Figures 1 to 3, the much-worn teeth of an old individual of Chi- 

 maera monstrosa are drawn. If the palatine and the mandibular teeth of this 

 species are compared with the same teeth of Callorhynchus smythii, or of the 

 very young of the other species of that genus, or even of the very young of 

 Harriotta, it will be seen that the two lateral ridges of each palatine and the 

 single lateral ridge of each mandibular are in the same positions, but in the 

 later stages of individuals of Chimaera the impact is applied to the forward 

 extremities of the ridges, and in the other genera mentioned it is exerted on 

 their sides. Yet if the account of the dentition of Chimaera is carried no 

 further it will be incomplete and misleading, for as the anterior edges and tritors 

 of the palatine and mandibular plates are ground away by use in aged indi- 

 viduals, the impact is more and more applied to the inner sides of these plates, 

 farther and farther backward. Consequently tritors develop, later in the lives 

 of such individuals, on the sides of calcigerous tubes the extremities of which 

 were the tritors of earlier stages. On the teeth, of a specimen of Chimaera 

 monstrosa more than thirty inches in length, shown on Plate 7, Figures 1-3, 

 the tritors of the forward edges are the only ones that appear; the ridges of 

 the inner sides are present, but evidently they had not served as grinders 

 and they bear no tritors. On old individuals of Chimaera colliei the tritors of 

 these ridges are prominent and more swollen than those of Callorhynchus 

 smythii, 1 late 6, Figures 1 and 2, and possibly in this or other species of 

 Chimaera they may with greater use become much expanded, or even may 

 become confluent somewhat as in most species of Callorhynchus. 



The Viscera. Plate 1, Figure 2 ; Plate 4, Figure 4 ; Plates 8 and 9. 



The stomach and the inside walls of the body cavity of Rhinochimaera 

 pacifica are blackish ; behiuil the stomach the intestines are lighter in color. 

 The alimentary canal is but little longer than the abdominal cavity ; the extent 

 of the difference in the two lengths is indicated in the short transverse portion 

 of the valvular section of the intestine in Plate 1, Figure 2. The distinctions 

 between the stomach and the intestine are not particularly well marked, though 

 the walls of the former are darker and are provided on the inside with longi- 

 tudinal folds or striae, less noticeable when distended, which disappear at the 

 pylorus. The intestine properly so called may be divided into two sections ; a 

 longer one containing the first turn of the spiral fold, which originates close 

 behind the stomach at the point of the entrance of the bile duct and as a mere 

 fold of the inner membranes, attached to the wall, gradually makes the turn as 



