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Show 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 already indicated in Davies's large figure, but still more satisfactorily shown in our Plate L V . fig. 1, 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 longitudinal row of comparatively large recurved booklets, upon inconspicuous 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 patcb 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 individuals that possess it ; for a number of blunt conical tubercles, without radiated bases, are clustered together upon its inferior aspect (h) to oppose the group of more slender booklets already described at the base of the snout. W h e n well preserved (as in no. I.), the surface of the spine exhibits the reticulate impressions of the vessels in a once enveloping integument1 ; and on each side there is a marked longitudinal groove (fig. 5, g), which gradually disappears on approaching the distal extremity. The peculiar form of the spine is also worthy of note, more particularly 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 chimreroid Ischyodus 2, 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 1 Mr. Boulenger has kindly helped me to determine that the corresponding appendage in the living Chimcera monstrosa is likewise covered with skin. 2 Sir P. Egerton, " O n a new Chimasroid Fish from the Lias of Lyme Regis (Ischyodus orthorhinus, d)>" Quart. Journ. Geol. Soc. vol. xxvii. 1871, pp. 275- 278, pi. xiii. 3 Sir P. Egerton, "Prognathodus Giintheri (Egerton), a new Genus of Fossil Fish from the Lias of Lyme Regis," Quart. Journ. Geol. Soo. vol. xxviii. 1872, pp. 233-237. 35* |