1910.] ANATOMY OF THE FRILLED SHARK. 567 



cartilage becomes thicker and more rounded, attaining its greatest 

 diameter at a point almost equidistant from each end. A groove 

 now appears on its dorsal surface to the right of the median line, 

 and gradually deepens toward the distal end of the cartilage. 

 This is the groove in the cartilage corresponding to the channel 

 in the musculature. 



In his account of the claspers, Giinther says that the groove is 

 on the ventral side of the axial cartilage, but how he arrived at 

 this conclusion it is very difficult to imagine, especially as he 

 figured it on the dorsal side. The groove is overhung in its 

 deepest part by the forwardly curved, tongue-shaped marginal 

 cartilage, R.v., which is attached basally to the outer border of 

 the stem cartilage, and at its distal end to the ventral terminal 

 cartilage, T.v. The latter and the corresponding cartilage, T.d., 

 on the inner side of the appendage have sharp, chondrified 

 cutting edges, and are movably attached to the lateral borders 

 of the distal end of the axial cartilage. The ventral terminal, 

 ■ T.v., is shorter than the dorsal terminal, T.d., and its anterior 

 end is more sharply pointed than that of the latter. The ridge 

 corresponding in position to the dorsal marginal cartilage, R.d., 

 of many other selachians is practically indistinguishable, and is 

 certainly not as well marked in the specimens which I have 

 examined as the ridge figured by Giinther. 



The lateral radials are mostly trisegmental and, in general, 

 they resemble those of the female pelvic fin, especially those 

 attached to the pelvic girdle. Of these, the proximal segments 

 are attached to the ventro-lateral edge of the girdle, and are 

 directed outward, obliquely downward, and in a slightly posterior 

 direction. They are flattened on their dorsal surface and the 

 three or four anterior ones exhibit fusion. Those attached to 

 the basipterygium are more rounded and gradually increase in 

 length as we approach the posterior end of the cartilage. The 

 last two or three are not segmented, and this is a further point of 

 resemblance to the condition prevailing in the female fin. There 

 are differences in the examples that I have examined in -the 

 extent to which the anterior radials exhibit fusion, and also in 

 the segmental or non-segmental chai-acter of the posterior ones. 

 In regard to the latter point, it will be seen from a comparison 

 of my figure with that given by Giinther, that whereas the last 

 three radials are not segmented in my figure, only the last is 

 complete in his. 



When the mixipterygium of Chlamydoselachtis is compared 

 with that of Hexanchus griseus, described and figured by Huber, 

 one is at once struck by the high degree of development pre- 

 sented by the organ in Chlamydoselachus. Whereas in Hexanchus 

 the axial cartilage is represented by a comparatively short 

 cartilage, scarcely distinguishable from a lateral radial, and 

 bearing no accessory cartilages ; the homologouspart in Chlamydo- 

 . selachus is a long, stout cartilage, furnished distally with three 

 movable accessory cartilages. 



