ACTINOPTERYGII. 101 



the development of fulcra is variable. The most characteristic 

 genus is 



Macrosemius. In this fish, as in other members of the family, the 

 basicranial axis is straight, and there is no ossified interorbital septum. 

 The cheek plates are very delicate ; the cleft of the mouth is horizontal, 

 and the rostrum does not project beyond the mandible. The sclerotic of 

 the eye is ossified. The teeth are styliform or conical, largest on the pre- 

 maxilla, vomer, and dentary. The opercular apparatus is complete, but a 

 gular plate has only hitherto been observed in the allied genus Ophiopsis. 

 The notochord is shown to have been persistent, without ring-vertebrae ; 

 the ribs are short and slender. The fins consist of very robust bifurcating 

 rays, without fulcra except in the caudal. The pectoral fins are much 

 larger than the pelyic pair ; the dorsal fin arises immediately behind the 

 occiput and extends continuously to the caudal pedicle ; the anal fin is 

 small, and the caudal rounded. The rays of the dorsal fin are sometimes 

 denticulated on their posterior border. The scales are thin, with peg-and- 

 socket articulation, and are apparently wanting towards the dorsal margin ; 

 those of the middle of the flank are largest, and some of the transverse 

 series bifurcate above. About four very large ridge-scales occur on the 

 lower margin of the pedicle at the base of the caudal fin. The typical 

 species is M. rostratm, attaining a length of about 0'3 m., from the Litho- 

 graphic Stone (Lower Kimmeridgian) of Bavaria. Other large species 

 occur on the same horizon in the Dept. Ain, France ; while diminutive 

 species are known both from the Upper Portlandian of the Dept. Meuse, 

 France, and from the Purbeckian of the Vale of Wardour, Wiltshire. 



The systematic position of the remarkable family of Pycno- 

 dontidae is uncertain, but it seems to be a specialized and partly 

 degenerate offshoot of the Lepidotus-like genera. These fishes 

 range from the Lower Lias to the Lower Eocene inclusive, and 

 are a remarkable instance of the persistence of a specialized 

 type a parallel to the case of the Ccelacanthidse already 

 described (p. 78). They are deep-bodied fishes (fig. 74) with 

 robust cranial bones, a small mouth and tritoral dentition 

 (fig. 72 a c), the opercular apparatus much reduced, and 

 the notochord always persistent without ossifications in its 

 sheath (fig. 72 d, e). The fin-rays are stout, articulated and 

 divided distally; fulcra are absent. Both pectoral and pelvic 

 fins are present, while the dorsal and anal fins are more or less 

 extended. The scales, when present, are rhombic, united by a 

 peg-and-socket articulation and strengthened within by a 

 vertical rib near the anterior border (fig. 72 f)\ they are 



