1886.] SQUALOKAJA POLYSPONUYLA. 533 



the two excavations at the base of the rostrum in the fragment 

 shown in Davies's fi». 4 evidently testify to their normal proportions 

 and situation. In a line with the prominence is fixed the base of 

 the rostral spine (r.s), quite at the hinder extremity of the ethmoi- 

 dal tract ; and still more posteriorly, the chondrocranium begins to 

 exhibit considerable lateral compression, though finally widening to 

 a slightly broader occiput. 



Extending backwards from the antorbital process, the slender 

 postpalatine cartilage (pt.pa) is preserved in most specimens 

 (especially in no. IV. fig. 2), but there is some uncertainty as to 

 whether it formed a distinct element. It tapers slightly to its distal 

 end, and the crushing during fcssilization has usually imparted to 

 it the deceptive appearance of connection with the hyomandibular. 



No postorbital process can be observed, and the circumstances of 

 preservation are probably accountable for the absence of any trace 

 of a fontanelle in the cranial roof ; but there is an interesting 

 V-shaped protuberance (a.v) close to the hinder extremity, evi- 

 dently representing a fold round the hollow into which opened the 

 aquecluctus vestibuli (or ductus endoli/mphaticus) of each auditory sac. 



On the ventral aspect, the parachordal, or " investing mass " 

 (fig. 3, iv.m), is produced posteriorly mto a pair of occipital 

 condyles {oc.c), as already noted by Riley ; and there is a well- 

 marked median ridge (w), obviously due to the remains of the 

 primitive notochordal sheath. A median foramen (c./) is also some- 

 what conspicuous, and, if not the result of accident during fossiliza- 

 tion, is evidently the passage for the united internal carotid arteries 

 proceeding to the pituitary body'. 



Of the mandil)ular and hyoid arches, the hyomandibular cartilage 

 (figs. 1, 2, hni) is the only portion satisfactorily preserved. In its 

 crushed condition it is seen to extend from each side of the occiput, 

 curving outwards and forwards, and gradually tapering to the distal 

 extremity. In shape it approximates to that of most " Batoidei," 

 being twice as broad proximally as distally, and its apparent conti- 

 nuity with the cranial roof is probably due to the process of fossili- 

 zation. Not a trace of the pterygo-quadrate and mandibular 

 cartilages appears exposed to view ; but the arrangement of the 

 dental plates in the specimen no. III. (fig. 3, t) shows that the two 

 rami of the jaw met at the symphysis in a comparatively acute angle, 

 and were not placed in the same straight line, as is the case in so 

 many living Rays. 



But the most remarkable feature to be noticed in the skull of 

 Squaloraja is presented in the two pairs of transversely elongated 

 appendages, with reflected ends, arising from beneath the narrow 

 part of the palato-trabecular region. These curious structures are 

 not well shown in our fig. 1 {ci.a, ci.b), but can be studied in their 

 entirety in the large specimens figured by Riley and Davies. The 

 most anterior {ci.a) is the larger, and is completely displayed on 

 both sides of the last-named fossil ; its total length is equal to three 

 times the width of the skull at the position where it emerges, 

 ' See T. J. Parker, ' Zootomy,' 1884, p. 62, fig. 20. 



