:810 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [64] 



crowded together centrally, they assume hexagonal or perhaps pentag- 

 onal forms. When they drop out and are lost, they leave quite a deep, 

 conical pit or socket behind them. Posterior to this dental area, the 

 parasphenoid lies horizontally, being convex from side to side, in order 

 to conform with the lower surface of the cranium. Behind, it is forked, 

 the limbs being carried backward to within a millimeter or so of the 

 posterior margin of the basioccipital. Between them we find a trian- 

 gular depression with its apex directed forward. Viewing the cranium 

 from this aspect, its posterior third is broad and of a quadrilateral out- 

 line, the figure being bounded in front by the postfrontals (Fig. 31, 

 Ptf.) ; laterally by the squamosals, and behind by the ex- and basioccip- 

 ital, opisthotics, and squamosals. Eiising in the center of this space, 

 mesially, is the portion formed principally by the prootics and basi- 

 occipital, being overlapped by the parasphenoid. This contains the 

 eye-muscle canal, with the braincase above it. Its form is well shown 

 in the figures I present of the lateral and inferior views of the cranium 

 of this fish. On either side of it occurs a deep conical indentation, about 

 which the various foramina pierce the bone to enter the brain-case. 

 These openings, and this great, blind, conical pit are bounded exter- 

 nally by the facet, on either side, for the hyomandibular. 



The rear view of the cranium of Ahula is an exceedingly interesting 

 study, presenting conditions that I have never observed in any other 

 fish. On the superior aspect of the cranium (Fig. 30 8. 0.) we saw how 

 the supraoccipital was wedged in between the parietals. From this 

 portion in the middle line, it throws backwards and downwards a 

 stumpy, triangular crest, composed for its greater part of two parallel 

 and vertical laminae, separated from each other by about a millimeter. 

 On either side of this the bone extends horizontally for a little distance 

 to meet the epiotics. These last elements may also be seen upon 

 superior view (Fig. 30 Ep. 0.). They there articulate with the squamo- 

 sals and parietals, and with the supraoccipital as just described. Each 

 epiotic from this position, is extended backwards as a stout horizontal 

 and triangular process, a peculiar tubercle being developed on its 

 superior surface. Beneath, and anteriorly, the under surface of this 

 process sends down a vertical plate, lying parallel to the median plane. 

 These two plates inclose a general concavity on the posterior aspect of 

 the cranium, which is partially divided in two by a vertical crest on the 

 supraoccipital which again is directly continued by the crest formed 

 through the uniting suture of the exoccipitals. The upper part of the 

 base of this concavity is composed of the vertical portion of the supra 

 occipital, while all the lower part is composed of the broad exoccipitals, 

 the cranium being held and viewed with the frontals upwards and in 

 the horizontal plane. Now, wedged in, in this concavity, on each side, 

 and outwards, we observe what first appears to be a separate and 

 nearly circular piece of bone, it being pierced by three foraminse. Towards 

 the median line it articulates with the supraoccipital and exoccipital. 



