148 W. Danes — On Squaloraia. 



covers the snout commences on tlie inside of these ridges, and is 

 there coarsely rugose. 



The next specimen to be noticed is a detached rostral spine (PL IV., 

 Fig. 3). It is five inches long, and lies on its side in the matrix: 

 the lateral expansions of the posterior end, and consequently the 

 articulating surfaces, are destroyed ; otherwise it is well preserved. 

 The posterior half is straight, the anterior half rises upwards by a 

 gentle curve to the apex. I assume this to be the normal form of 

 the spine ; if so, it is important, as proving that it could not have 

 been united to the straight snout ; and also, that the examples which 

 are in place on the head (PL IV., Figs. 1 and 5) have been straight- 

 ened by vertical pressure. On either side is a groove, which extends 

 from the base nearly to the anterior end ; probably a vascular canal. 

 The inferior surface is slightly rounded, excepting a small portion 

 of the proximal end, which is flat or very shallowly depressed. It is 

 well ossified, and has the radiated tubercles isolated and irregularly 

 disposed upon its upper surface, most numerous at the posterior end, 

 whence they become more sparse, and also smaller, until they finally 

 disappear at a short distance from the apex. 



The position of this spine on a Plagiostomous fish was anomalous, 

 and the purpose to which it could be applied difficult to determine, 

 as I knew of no analogue among this order of fishes. For although 

 its form and structure might suggest its having been an organ of 

 defence, yet the position upon the head, and its manner of attach- 

 ment, which could only allow of its elevation at a low angle, 

 and therefore but little above the plane of the lower and longer 

 snout, would preclude its having been applied to such use. I 

 determined therefore to submit the specimens, and the views I had 

 arrived at respecting them, to Dr. A. Giinther, F.E.S., of the Zoolo- 

 gical Department, British Museum. After careful examination 

 he confirmed my conclusions, and added that the analogue was to be 

 found in the ChimceridcB ; and, moreover, that the specimens were the 

 remains of males, and that in all probability, sooner or later, the 

 female would be found. This valuable suggestion, for which I am 

 much indebted to Dr. Giinther, cleared up a difficulty I had experienced 

 in placing the third of the before-mentioned specimens with the 

 present genus (see PL IV., Fig. 4) ; for although it has the 

 general form and character of the head of Squaloraia, it has no 

 indication of ever having possessed a spine, as there is no transverse 

 suture, nor ridge for its articulation ; and the part corresponding to 

 the interspace in the male is covered by the shin, which is unbroken 

 from the occipital region to the end of what remains of the snout; 

 this is imperfect, the anterior extremity, as in all the other specimens 

 that have come under my notice, being absent. The cartilaginous 

 processes which form its boundaries are extremely slender, mere 

 threads, possibly suggestive of considerable flexibility ; and the 

 snout (judging from what remains of it) is, relatively to the head, 

 much smaller than in the male. A considerable portion of the 

 cranial cartilage is preserved, and also a part of the left orbit. 

 The entire length is 4^ inches ; from the occiput to the expanded 



