230 NORTH STAFFORDSHIRE COAL FOSSILS. 



GENUS RHOMBOPTYCHIUS, HUXLEY. (Ref., Quar. Jour. 

 Geol. Soc., vol xxii., p. 604.) 



This genus was established from specimens collected 

 in this coal-field. According to Dr. Young (op. cit.) 

 " the scales vary from cordate-ovate to rhombic ; 

 the length in the former case exceeds the breadth : 

 in the latter the reverse holds. In both forms the punctate 

 free surface is ornamented with coarse straight ridges which 

 follow the outline of the sides, meeting at an angle posteriorly, 

 and thus giving a rhombic aspect to the scale." Our 

 collection contains several fine examples of the cranial shield. 

 They are solid : the parts are united by well-marked sutures. 

 The inner posterior orbital border is preserved, but not the 

 outer border. One of these specimens exhibits the upper 

 surface of the cranium, which is ornamented with coarse 

 tubercles. There are others in which the ornamentation 

 consists of fine rounded ridges more or less confluent, the 

 surface of the bone being finely reticulated, the jugular 

 plates and opercular being similarly ornamented. The 

 specimens hitherto discovered are too fragmentary to enable 

 .us to determine whether these and other differences are of 

 specific importance. One or two fragments of mandibles 

 have occurred. One of these, in our collection, shows that 

 this bone was of great strength. Both ends of the jaw 

 are imperfect, but the general arrangement of the teeth is 

 similar to that in the same bone in Megalichthys, to which 

 genus this fish is closely allied. In our specimen, one large 

 and perfect tooth and the base of a second tooth are shown. 

 The large tooth is straight and plicate at the base : about 

 the middle of the tooth there are two rings of short, longi- 

 tudinal depressions. The outer dentary margin is set with 

 small, conical teeth. Many large vertebra of Rhomboptychius 

 have been found : they are thin osseous rings, some of them 

 an inch and a half in diameter. 



