1887.] PROF. T, J. PARKER ON CARCHARODON RONDELETII. 31 



inserted between the bases of adjacent neural arches, the latter {n.a) 

 forming the whole dorsal region of the neural tube ; whereas in the 

 remaining greater part of the column the intercalaria form actual 

 interneural arches. 



The tail-fin contains nearly three-fourths as many vertebrae as all 

 the rest of the column, the lO/th centrum being the first of the tail- 

 fin (Plate VI. fig. 12, vert. cent. 107), recognizable by being the first 

 to develop a hsemal spine. In this and the five following vertebrae 

 the haemal spine (Jme.sp) is a separate cartilage, quite distinct from 

 the hsemapophyses ; in the remaining tail-vertebrae the two are 

 continuous. The haemal spines gradually increase in length to the 

 120th vertebra, and then undergo progressive diminution : the 

 longest, in specimen A, is 10 cm. in length. 



The tail-fin is thus supported ventrally by haemal spines : the 

 small portion lying dorsad of the vertebral column, on the other 

 hand, has its framework constituted by a series of cartilages {ptg) 

 which are evidently not neural spines but pterygiophores ^ or carti- 

 laginous fin-rays. These have no definite relation to the vertebral 

 segments, one of them sometimes corresponding to a single vertebra, 

 sometimes to two, and sometimes to three. 



Hasse remarks that while intercalaria are absent in the haemal tube 

 in the caudal region, they are present in the neural tube, which has 

 therefore double neural arches as in the trunk region. This is true 

 only as far back as the iSOth vertebra (vert.cent. 130), caudad of 

 which intercalary pieces are absent and the neural arches conse- 

 quently single. 



In the 167th (vert.cent. 167) and following vertebrae, the neural 

 and haemal arches are united with one another on each side by a verti- 

 cal bridge of cartilage, so that the middle portion of each centrum is 

 hidden. From the 175th vertebra to the end of the series there are 

 no longer distinct neural and haemal arches, but simply an irregular 

 vertical plate of cartilage, in which the last eight (?) vertebral bodies 

 are imbedded. An examination of this region in the fcetal specimen 

 (E) shows (Plate VIII. fig. 28) that these are all perfectly formed 

 centra except the last, which is a somewhat irregular mass of hone, and 

 appears to me to be a demi-vertebra ^ i. e. to represent the anterior 

 half of a centrum formed in the posterior moiety of the last meso- 

 blastic somite. 



In the skeletons of A and B the neural and haemal arches are 

 entirely uncalcified ; in the large specimen C there are small calcific 

 patches on the anterior neural arches only ; from about the 4th or 

 5th vertebra backwards the only calcifications are those of the centra. 



b. The Skull. — The cranium is described in detail by HaswelP, 

 who gives figures of it from above and from the right side, which 

 are, however, too small to show certain important details, such as 

 the nerve-foramina. For this reason, and because of the desirability 



^ T. J. Parker, "On the Skeleton of Ecgalccus argenteus," Trans. Zool. Soc. 

 vol. xii. p. 24, note. 



2 Cf. " Skeleton of Rcgalectis," p. 22. 



^ Op. cit, Journ. Linn. Soc. N. S. W. vol. ix. p. 15. 



