1886.] SQUALORAJA POLYSPONDYLA. 531 



the specimens numbered I. and III. reveal a few hitherto unnoted 

 facts concerning the arrangement of the small prickly tubercles. 



As alread}^ indicated in Davies's large figure, but still more satis- 

 factorily shown in our Plate LV. fig. I, a series of the tubercles with 

 especially long recurved booklets is arranged along either edge of 

 the prenasal (intertrabecular) cartilage ; and these two rows are 

 precisely parallelled in the snout of certain living species of Bhino- 

 batus (e. g. R. granulatus) . But immediately at the base of the 

 rostrum, where the cartilage is particularly firm and expanded into 

 two lateral elevations (Davies, fig. 2), the tubercles become densely 

 clustered in a manner not observable in the existing form ; and this 

 arrangement is in intimate relation with the overlying spine. The 

 disposition of the tubercles along the trunk, even if originally regular, 

 is now no longer evident, and none but scattered examples are to be 

 seen ; but the slender tail was provided on each side with a longi- 

 tudinal row of comparatively large recurved booklets, upon inconspi- 

 cuous bases, as is very well shown in the female, no. III. (fig. 7). A 

 small tuft of these dermal structures also occurs at the extremity of 

 each clasper in no. I. (fig. 1, hk), and there are distinct indications 

 of a patch of very minute prickles upon the membranous portion of 

 the (right) ventral fin in the same specimen. 



In regard to the rostral spine, Davies's figures and descriptions 

 leave little to be added. The conclusion as to its absence in certain 

 individuals (females) is confirmed in an interesting manner by the 

 fossil no. III., which has been so "developed" on the dorsal aspect 

 that there cannot remain the slightest doubt upon the subject. But 

 a new specimen, from the Enniskillen Collection (no. V. fig. 5), still 

 further demonstrates its prehensile character in the indi\iduals that 

 possess it ; for a number of blunt conical tubercles, without radiated 

 bases, are clustered togetlier upon its inferior aspect (/i) to oppose 

 the group of more slender booklets already described at the base of 

 the snout. When well preserved (as in no. I.), the surface of the 

 spine exhibits the reticulate impressions of the vessels in a once 

 enveloping integument ^ ; and on each side there is a marked longi- 

 tudinal groove (fig. 5, g), which gradually disappears on approaching 

 the distal extremity. 



The peculiar yo>-»z of the spine is also worthy of note, more parti- 

 cularly as it is repeated in two other cartilaginous fishes whose 

 remains have been found in the same geological formation ; it differs 

 but little from that of the rostral appendage in the chinueroid 

 Ischyodus ^ and is still more similar to another Liassic spine which 

 there is some reason for suspecting may belong to the remarkable 

 Prognathodus ^. The peculiar shape, indeed, taken together with 



^ Mr. Boulenger has kiuclly helped me to determine that the corresponding 

 appendage in the living Chimara monstrosa is likewise covered with skin. 



■^ Sir P. Egerton, " On a new Chimaroid Fish from the Lias of Lyme Regis 

 {^hchyodas orthorhinus, J)," Quart. Journ. Geol. Soc. voL xxvii. 1871, pp. 275- 

 278, pi. xiii. 



^ Sir P. Egerton, " Prognathodus Giintheri (Egerton), a new Genus of Fossil 

 Fish from the Lias of Lyme Eegis," Quart, Journ. Geol. Soo. vol. xxviii. 1872, 

 pp. 233-237. 



35* 



