A. Smith Woodivard — On a Liassic Fish. 205 



proved to belong to Osteorachis by its characteristically clustered 

 slender teeth ; and the writer is indebted to Professor A. H. Green, 

 P.R.S., for facilities to make a detailed study of it. 



The specimen in question is preserved in indurated Lias, and much 

 fractured by crushing. It is laterally compressed, and at the same 

 time somewhat distorted, so that the jaws on the left side are opened 

 and parts of the inner dentition are exposed. This left side presents 

 the features of greatest interest, and it is shown of two-thirds the 

 natural size in PI. VII, Fig. 10. The cranium itself is too imperfect 

 for description, but its roof is observed to have been in part very finely 

 tuberculated. There is an ossification in the postfrontal (sphenotic) 

 region {pt.f.), and the same remark applies also to the prefrontal 

 (lateral ethmoidal) region {p-f.)- The orbit in the fossil is occupied 

 by a fragment of the ossified sclerotic {scl.). The cheek is shown 

 to have been completely covered with plates to the border of the 

 preopercidum, and several of these exhibit traces of a very fine 

 tuberculation, while other portions are more coarsely rugose. Two 

 very large postorbitals {pt.o.) are distinct, and there are also remains 

 of a circumorhital ring [c.o.). Within these fi'agments above the 

 maxilla can also be seen portions of a large thin smooth plate, 

 which is not improbably the entopterygoid. The maxilla [mx.) is long 

 and slender, fractured in two places, and either destroyed or obscured 

 at its anterior extremity. It is stout in front, thin and slightly 

 deepened behind, with its outer surface partly smooth, partly rugose. 

 Its hinder third is overlapped by a small elongated supramaxiUa 

 [s.tnx.) which is deepest posteriorly, acutely pointed in front, and 

 exhibits a finely tuberculated external surface. Its oral border is 

 nearly straight for the greater part of the length of the element, but 

 there is a downward trend behind, perhaps exaggerated in the fossil 

 by the accidental splitting of the bone. Its teeth are all long and 

 slender, nearly of equal size, well spaced and arranged in a single 

 series. They are enamelled to the base and distinctly hollow. The 

 premaxilla [p.mx.) is only obscurely indicated, but extends for a 

 considerable distance along the oral margin, and bears probably not 

 less than ten long slender teeth, similar to those of the maxilla ; seven 

 of these teeth are preserved. The left mandibular ramus, showing 

 the high coronoid region, is also fragmentarily preserved, and the 

 dentary (d.) bears a single series of teeth, like those of the margin 

 of the upper jaw, and not exceeding the latter in size. Most of these 

 teeth are displaced or broken away, and cross-sections of the bases of 

 some are exposed. The great interest of the jaws, however, centres 

 in the streak of clustered dentition both immediately below the 

 maxilla and immediately above the mandible, but distinctly internal 

 to each. The teeth of these clusters are shown to be exactly similar 

 to those on the margin of the jaw, but much smaller and more closely 

 arranged ; and they all appear to be readily broken off the bones 

 supporting them. The upper cluster (ecpt.) doubtless pertains to 

 the ectopterygoid, while the lower cluster (spl.) may be referred with 

 certainty to the splenial. Between the rami of the mandible there 

 are remains of a large gular plate {gu.) in front, and a few branchio- 

 etegal rays (Jr.) behind. 



The characteristic inner teeth not only serve to identify the skuU 



