140 chim.5;roid fishes and their development. 



brain was shaped like that of a shark. Of dental plates (fig. 120) there are three 

 pairs; the meckelian and palatines resemble one another closely, thus suggesting 

 the doubtful Devonian forms. In front of the palatines now occur, for the first 

 time among Chimjeroids, a pair of "vomerine" plates, oblong and tumid. In these, 

 as in the other dental plates, tritors occur, in the form of conspicuous lamellae. The 

 mouth was probably delicate and, judging from the position of the dental plates, 

 it opened widely, far more shark-like than in any recent Chimseroid. At either 

 side of the mouth region appear three conspicuous outgrowths, fibro-cartilaginous in 

 structure, forming together the marginal framework of this region of the head. These 

 structures, although shown in many specimens, are none the less too imperfectly 

 preserved to warrant a definite conclusion as to their relations. By some authors 

 they have been regarded as spines, by others as direct outgrowths from the trabec- 

 ular region of the cranium. The anterior pair may represent the paired rostral 

 cartilages of recent forms. The two posterior pairs are possibly labial cartilages. 

 A conspicuous rostrum is present, unjointed at its base, and defended on the dorsal 

 side by marginal rows of stout dermal denticles (fig. 139). Adjoining the rostrum 

 the snout was narrowed, and in this region were apparently areas representing 

 the pellucid spaces on either side of the rostrum in recent Chimseroids and in such 

 selachians, for example, as Rhinobatus and many rays. In the occipital region of 

 the cranium a large, median, elliptical fosse was present, at the base of which there 

 were probably openings into the otic region. Below this fosse one can sometimes 

 trace the anterior end of the column, advancing into the floor of the cranium as far 

 forward as between the orbits, and showing even in this region ring-like peripheral 

 thickenings. It is interesting in this connection to observe that a well-marked 

 occipital joint was present between cranium and column, and that in a single 

 specimen (Harvard Museum No. 1147, Pal. Coll., which through the kindness of 

 Dr. Eastman was generously loaned me) the anterior portion of the column shows 

 traces of a coarser segmentation, which indicates, outwardly at least, cyclospondy- 

 lous vertebrae (fig. 138 a). 



In dermal characters Squaloraja was distinctly shark-like. The entire body 

 was covered more or less thickly with shagreen, and at certain points the denticles 

 attained considerable size, e. g., on the sides of the rostrum, near the base of the 

 clasping spine (detail in fig. 139), along the sides of the tail, on the dorsal side, 

 near the base of the paired fins, on the clasping organs, and almost as spines in the 

 suborbital region. Here they form so firm a mass that the ring below the eye is 

 preserved as a conspicuous character of the fossil. 



Girdles and the cartilaginous supports of the paired fins are distinctly Chimse- 

 roid, c. g. , in location and proportions. The stoutly developed shoulder-girdle is 

 similar in form to that of a recent genus; it is not known whether the bi-basal 

 arrangement of the basalia occurs in the pectoral fin, but it is certain that the radial 

 cartilages, about 30 in number, are arranged in a manner strikingl}' like those of 

 Chimsera; their marginal extension was also modern in plan. In the ventral fins, on 

 the other hand, more conservative conditions prevail, for the radial cartilages were 

 probably 18 to 20 in number (about one-third more numerous than in recent forms), 



