18 



nine rays of the ventral fin. There are ten interim-null spines, articulated to the tenth and 

 fourteenth heemal spines inclusive. The first of these interhsemal spiues is very short and 

 much expanded transversely at its distal end : the rest are less expanded there, and are modi- 

 fied to articulate with dermoheemal spines, which form the eleven rays of the anal fin. The 

 first four of these rapidly increase in length, and in the first and second the lateral moieties 

 have not coalesced. 



The bones of the head are numbered on coloured labels showing their special and general 

 homologies, according to the Tables I. and II. 



The basisphenoid underlaps the basioccipital as far as its articulation with the atlas, with 

 the centrum of which the bases of the exoccipitals likewise articulate. The supraoccipital is 

 a short thick spine, and the paroccipitals develope similar rough processes for the attachment 

 of the suprascapulars ; each of these bones likewise sends a short straight process to join the 

 mastoids. The petrosal appears externally at the back part of the skull, wedged between 

 the exoccipital, paroccipital and mastoid. The parietals are small and divided from each 

 other by the interparietal portion of the superoccipital, which joins the back part of the large 

 frontals. There is a wide vacuity between the parietal, paroccipital, mastoid and frontal, 

 analogous to that which is closed by the squamosal in mammals : it is filled up by cartilage 

 in the recent fish. 



There are two small dermal ossicles on each side between the superoccipital spine and the 

 suprascapula. The scapula, as in other osseous fishes, is a simple rib-like bone : the cora- 

 coids are long, expanded, and unite together below to complete the scapular arch, without 

 the intervention of a median piece. The humerus is articulated to the middle of the back 

 part of the coracoids by a transversely elongated extremity. It is also expanded at the distal 

 end where it articulates by cartilage with the ulna and radius. 



The ulna is a semicircular plate of bone perforated in the centre, and, besides its articula- 

 tion with the humerus, the radius and the ulnar carpals and metacarpal ray, it also directly 

 joins the broad coracoid. The radius, after expanding to unite with the humerus, the ulna 

 and the radial carpals, sends a long and broad process downwards and inwards which is 

 united by ligament with its fellow and with the lower termination of the coracoid. A basis 

 of adequate extent and firmness is thus ensured for the support of the pectoral fins. The 

 carpal bones of these fins are four in number, progressively increasing in length from the 

 ulnar to the radial side of the wrist. 



The metacarpo-phalangial rays are thirteen in number ; the uppermost or ulnar one being 

 the strongest and articulating directly with the ulna. The base of each ray is expanded and 

 bifurcate. They slightly increase in length from the first to the third, and then gradually 

 diminish to the lower or radial border of the fin. 



The broad epitympanic articulates by a continuous joint with both the mastoid and post- 

 frontal. It presents an articular surface at its posterior margin for the opercular bone which 

 is subquadrate ; the two posterior borders meeting at a right angle to form the obtuse 

 posterior angle. The convex margin of the subopercular is directed as much backwards as 

 downwards ; the vertical diameter of the interopercular is the longest ; the posterior border of 

 the preopercular is gently and almost equally convex. 



The short stylohyal is attached to the cartilaginous interspace between the epi- and meso- 



