70 PROCEEDINGS OF THE ACADEMY OP 



a marine formation. The two fishes, apparently extinct species and genera, 

 not previously noticed, are indicated by the remains briefly described as 

 follows : 



Oncobatis pentagonus (Ovxoc, a boss or tumor; Pane, a ray). Founded on 

 a dermal boss, with a pentagonal outline, the sides of which are convex. 

 Under surface strongly convex. Upper surface with five planes sloping from 

 a central summit and defined by as many prominent borders. From the sum- 

 mit an oval enameloid areola occupies rather less than half the extent of the 

 upper surface. The areola is shining, nearly smooth, and exhibits concentric 

 lines of structure. The very summit of the boss appears composed of a 

 harder, more translucent substance protruding through the opaque white 

 areola. Greater diameter of the boss, 16 lines; shorter diameter, 15 lines; 

 thickness from summit, 8 lines; greater width of areola, 8 lines; shorter 

 width, 6 lines. 



Mylocyprincs robustus Founded on specimens of pharyngeal bones with 

 teeth. There are eight of them of different sizes, all imperfect. The largest 

 have been double the size of the smallest, and perhaps they may have per- 

 tained to several species. They are robust, and indicate a large and powerful 

 fish. They have the general form of the posterior pharyngeals in the carp and 

 other cyprinoids. The posterior ramus is prolonged above in a stout pedicle, 

 with an inner triangular articular surface for attachment to the cranium. Its 

 posterior suiface, below the pedicle, is broad, nearly flat, with the outer bor- 

 der convex and acute, the inner border concave and sustaining a single row 

 of teeth. 



The anterior ramus is thick, and abruptly narrows forward, but is broken 

 at its fore part in all the specimens. At the angle of conjunction of the rami 

 the bone is massive, thicker fore and aft than transversely. The outer border 

 of the bone forms two flexures. The antero-external surface is broad, verti- 

 cally concave, transversely convex, in some cases entire, in others excavated 

 into pits communicating with the bottoms of the teeth or extending through 

 the bone where the latter have been shed. / 



The teeth form a single vertical row of four, and are supported on the inner 

 side of the conjunction of the two rami of the pharyngeal bone, projecting a 

 short distance below the level of the inferior ramus, and extending rather 

 more thau half-way up the superior ramus. They have stout bony bases, and 

 are of the true masticatory type. They bear a striking resemblance to human 

 premolar teeth the largest in size as well as form. They are all of the same 

 character, or present no variety. They successively increase in size from be- 

 low upward. The crown of the teeth is transversely oval, with a broad tritu- 

 rating surface depressed at the centre. The enameloid structure is everywhere 

 smooth. 



In all the specimens the uppermost tooth has been shed and not replaced, 

 its position being indicated by a large quadrate pit of the pharyngeal, in some 

 specimens extending through the bone. In most of the specimens the teeth 

 are but little or scarcely worn. In one specimen they are half worn away, 

 very obliquely from within, outward and forward. Measurements from several 

 specimens are as follow : 



Lines. Lin. Lin. Lin. Lin. Lin. 

 Length of posterior ramus to level of middle 



of second tooth 22 



Width on level of third tooth 8 8 7 6 5 



Thickness on level of second tooth 11 9 9 7 6| 



Length of series of four teeth. 13 12 8 



Transverse diam. of first tuoth 1\ 2 



" " second tooth 4 4 2.V 



Vertical diam. " ; < 2;] 2] l| 



Transverse diam. of third " 4.1 4 A\ 3h 



Vertical " " " 3i 3 _ 3\ 3" 



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