1910.] ANATOMY OF THE FRILLED SHARK. 553 



posterior ampulla ; and an upper one, the ramulus negleclv.s, 

 which curves upward toward the ductus utriculo saccularis 

 posterior. 



In structure and in the distribution of the nerve-supply the 

 membranous labyrinth of Chlamydoselachus resembles rather 

 closely that of Notidanus (Hexanchus) griseus figured by 

 Stewart (30). 



Y. Vertebral Column. (Plates XLIII.-XLV. figs. 9-17.) 



The notochord is persistent, and reaches from the pituitary 

 fossa in the basis cranii to the extreme tip of the long tapering 

 tail. There is an elastic supradorsal longitudinal ligament 

 which extends from the back of the cranium to a point just 

 posterior to the dorsal fin, where the dorsal supports of the caudal 

 fin commence. The number of vertebra?, as determined by 

 neuromeres, is one hundred and twelve, and this number includes 

 the irregular region at the extreme tip of the tail — to be dealt 

 with in detail later. In determining this number, I have counted 

 the ventral root foramina of the spinal nerves carried by the 

 basidorsals, as these are larger than the dorsal root foramina. 

 Moreover, the first foramen at the anterior end of the column is 

 a ventral one. The vertebral elements present, named according 

 to Gadow's (9) nomenclature, are as follows : — 



Dorsalia : basidorsals, interdorsals, and suprabasidorsals, the 

 last-mentioned being segmented off from the apices of the basi- 

 dorsals. The dorsal radial supports of the caudal fin I do not 

 consider as dorso-spinalia, because at their commencement an- 

 teriorly they are not always continuous with the neural arches, 

 and, moreover, there is as much evidence to show that in general 

 they originate independently of the vertebral column as there is 

 in favour of their being portions segmented off from the dorsalia 

 below them. 



Ventralia : basiventrals, interventrals, ribs, and haemal arches, 

 and ha?mal spines in the caudal region. 



I have been unable to find the calcifications which Garman 

 mentions as occurring in the mouths of the foramina for the spinal 

 nerves. No trace of them can be detected even after carefully 

 cleaning away the connective tissue which closely invests the 

 vertebral column. In fact, it would be somewhat surprising if 

 such calcifications were present, considering the small amount of 

 calcareous secretion found in the skeleton at all. 



It is perhaps worthy of note that, in the largest specimen 

 examined, the vertebral column over the abdomen was not 

 straight, but was contorted so as to have an undulating outline- 

 in the horizontal plane. Whether this was due to abnormal 

 growth or to the action of the preservative I do not know, but I 

 am inclined to the latter view. 



In connection with the formation of centra, my investigations 

 have revealed a number of points which Garman did not observe, 



