ACTIXOPTERYGII. 107 



margin of the jaw, and has a narrow upwardly-directed process near the 

 middle of its superior border. The lower end of the hyomandibular meets 

 both the quadrate and symplectic. The mandibular ramus exhibits the 

 usual elements, and the splenial enters the symphysis. The teeth on the 

 dentary are relatively large in a single spaced series, those of the premax- 

 illa and maxilla smaller and more closely arranged ; those clustered on the 

 voiner are also powerful, but most of the inner teeth are minute or even 

 granular. A large gular plate covers the whole of the space between 

 the mandibular rarui in front of the branchiostegal rays. The vertebral 

 elements are never more than separate hypocentra and pleurocentra, and 

 in the abdominal region the delicate ribs are articulated with short pro- 

 ia on the former. The large neural spines are free in the abdominal 

 region. There is a single pair of transversely-extended suprateraporal 

 plates, and immediately behind these the large triangular post-temporals 

 are observed. The fulcra on all the tins are biserial. Each scale is 

 strengthened on its inner face with a vertical median rib ; and the 

 principal flank-scales are united by a peg-and-socket articulation. The 

 typical species is Eugnathw orthostomus (fig. 75) from the Lower Lias of 

 Lyme Regis, Dorsetshire, and the genus ranges upwards as far as the 

 Lithographic Stone (Lower Kimmeridgian) of Bavaria, in which several 

 forms occur. 



FIG. 76. 



furcatus ; restoration, scales omitted, about one-eleventh nat. size. 

 U. Jurassic (Lithographic Stone); Bavaria. (From Brit. .!/(. Catal.) 



Caturus (tig. 76). A fish apparently only differing from Eugnathus in 

 two particulars, viz. (i.) the delicate character of the deeply overlapping 

 scales, most or all of which have lost the inner rib with peg-and-socket 

 articulation, and (ii.) the reduction of the teeth on the anterior half of the 

 splenial to a single series. Some of the chondrocranial elements are known. 

 In advance of the basipterygoid process of the paraephenoid there is a 

 very large zilisphenoidal ossification, much exceeding in size either of the 

 otii-s behind. The pro-otic is equally well ossified, and the opisthotic is 

 still more robust ; but no undoubted traces of pterotic and opisthotic 

 ossifications have hitherto been observed. The nasals resemble those of 



