88 C. R. Eastman — Tamiobatis vetustus. 



The olfactory capsules (zY) are slightly abraded along the 

 anterior margin, and it is impossible to detect a suture between 

 them and the antorbital spurs (A 0). On the other hand, there 

 is a small cleft, which might easily be mistaken for a suture, 

 passing across each of the postorbital processes in a longitudi- 

 nal direction. But these fissures have every appearance of 

 being fortuitous, and moreover show tool-marks along the 

 edges where they were probed into before reaching the hands 

 of the present writer. Although of unusual size for post- 

 orbital processes, we 'have no choice but to regard them as such ; 

 for, if suturally united with the cranium, they can be homolo- 

 gized w T ith nothing else than the metapterygoid, an element 

 with which they agree neither in shape, size, nor point of 

 attachment. Again, if it were possible to detect sutures here, 

 like indications ought also to exist where the antorbital 

 processes are attached. Granted that they are postorbital 

 processes (" sphenotic " Parker), their size and distal expansion 

 may be accounted for, perhaps, by supposing that membranes 

 were attached to them for the support of the anterior gill 

 arches or other structures. They slant outward and downward 

 so as to occupy 7 the same level, distal ly, as the tips of the 

 antorbital processes, 



The hyomandibular was presumably attached along the sinus 

 marked HM. Bounded on either side by prominent occipital 

 condyles was the foramen magnum (FM), and here the chon- 

 drification was very dense. Just back of the capsules for the 

 eyes on either side is to be seen a small reentrant angle in the 

 cranial wall. The cartilage is quite thick in this vicinity, and 

 appears to have been eroded by natural causes in the first 

 instance, and further pricked away with the needle so as to 

 produce the effect indicated. It is rather curious that acci- 

 dents of fossil ization and weathering should have affected both 

 sides of the object symmetrically in so many particulars. 



The nerve openings are readily identifiable, and have been 

 lettered to correspond with the classic illustrations of Gegen- 

 baur* and Parker, f The superior opening of the ethmoid 

 canal is at ce, that of the preorbital canal at op' ; cs marks the 

 foramina supraorbital, present here in two pairs only ; and 

 aa.v. is the aqueductus vestibuli. All of these openings are 

 very distinct, and their walls densely chondrified. 



Probable relationships and systematic position. — If remains 

 of the dentition or dermal ossifications had been preserved in 

 connection with the present specimen, or if skeletons of other 



* TJntersuchungen zur vergleichenden Anatomie der Wirbelthiere, Heft III. 

 Das Kopfskelet der Selachier, 1872. 



f On the Structure and Development of the Skull in Sharks and Skates (Trans. 

 Zool. Soc. London, vol. x, pt. iv), 1878. 



