30 PROF. T. J. PARKER ON CARCHARODON RONDELETII. [Jan. 18, 



Hasse ^ and a briefer account of the entire skeleton is given by 

 Haswell ^. I shall therefore confine myself to a few points which 

 do not appear to have been insisted on, mentioning especially such 

 as seem to be important for comparison with Lamna. 



a. The Vei-tebral Column, — In specimen A there are about 

 182 vertebral centra; at the end of the tail it becomes difficult to 

 count them accurately. The centra agree with Hasse's description, 

 except that I do not find the difference in the disposition ol' the 

 radiating lamellae of bone which that author give^ as distinguishing 

 the trunk- from the tail-vertebrEe. Hasse describes and figures only 

 two very thick dorsal lamellae in the caudal vertebrae, between the 

 origin of the neurapophyses : in my specimens there are three or 

 four comparatively thin lamellae as in the trunk-vertebrae {cf. figs. 

 13 and 14, Plate Vl.). 



One point not very clearly brought out by Hasse is the extreme 

 irregularity in the segmentation of the neural tube and of the 

 haemal tube or ridges. These are, in the embryo, continuous 

 cartilages ^, which undergo segmentation at a later stage than the 

 centra, becoming divided into vertebral portions, the neur- and 

 haemapophyses, and intervertebral portions, the interneural and 

 interhaemal pieces, or intercalaria. The irregular way in which 

 this segmentation takes place in Carcharodon is very striking, and 

 is well shown in figs. 7 and 8 (Plate V.), the former representing a 

 portion of the neural tube seen from above, the latter a portion of 

 one of the haemal ridges seen from below, Occasionally the distal 

 portion of a haemapophysis becomes segmented off, forming a rib 

 (fig- 8, r). 



Another matter not touched upon by Hasse is the modification 

 undergone by the vertebral column at its anterior and posterior 

 extremities. Anteriorly there is no clear line of demarcation between 

 skull and vertebral column. At the level of the third vertebral 

 centrum (fig. 6, vert.cent. 3) the neural tube meets on each side 

 with the corresponding hasmal ridge, forming a continuous lateral 

 investment of cartilage over the first two centra, which are thus only 

 visible from beneath. The continuous lateral cartilage thus formed 

 passes insensibly into the exoccipital region of the skull, while the 

 first and second centra pass into the basioccipital region, and the 

 neural tube into the supraoccipital region. Thus, when the .skull 

 is separated artificially from the vertebral column in such a way as 

 to leave intact the great parotic processes (fig. 1, p.ot.pr), the 

 plane of section passes naturally between the second and third 

 vertebral bodies, and the first two centra appear to be imbedded in 

 the basis cranii (fig. 3). 



It is also worthy of notice that in the first few vertebral segments 

 the intercahiry pieces (fig. ti, i) are small triangular processes 



^ Das natiirliche System cler Elasmobranebier. Jena, 1879. 



^ " Studies on the Elasmobranch Skeleton," Proc. Linn. Soc. N. S. W. vol. ix. 

 (1884) p. 3. 



' Baffour, ' Comparative Embryology,' vol. ii. p. 454. (Memorial edition, 

 vol. iii. p. 650. 



