Osteology of Catuvus and Osteoraclils. 381 



viewed from below in the fossil (PI. X. fig. 1 a) some of its 

 characteristic features can he distinguislied. The opisthotic 

 (op.o.) is a well-formed bone, with the usual large oval 

 foramen for the exit of the vagus nerve, and in front it 

 clearly articulates by a wavy suture with the equally well 

 ossified pro-otic {pr.o.), which is broken away anteriorly. 

 The postfrontal or sphenotic {pt.f.) is also massive and 

 distinct, with a very well-defined hinder border for union 

 with the rest of the upper part of the otic capsule, which 

 seems to have remained unossified, as in Amia. Tliere may 

 have been a granular calcification of the cartilage here, but 

 nothing more. The ossifications and calcifications in the 

 interorbital region of the chondrocranium are almost entirely 

 broken away, but there are just traces of the interorbital 

 septum (s.), showing the anterior production of the cerebral 

 cavity for the passage of the olfactory nerves. On the left 

 side of the fossil there are also indications of a robust pre- 

 frontal or ecto-ethmoidal ossification. 



The imperfect separated basicranial axis cannot be fitted to 

 the rest of the fossil, and the sutures between its component 

 elements are not distinguishable. The robust parasphenoid 

 is, indeed, firmly fused at least with the basioccipital. Tliis 

 basal membrane-bone exhibits a slight cleft beliind and is 

 expanded in front in the usual manner for squamous union 

 with the vomers ; it does not bear teeth, but there is an irre- 

 gular bony excrescence a little behind the middle, where 

 small teeth usually occur in allied fislies. The upper or 

 cerebral aspect of the specimen is interesting on account of 

 the configuration of the basioccipital. This bone is not 

 curved upwards at the sides, but agrees exactly with the 

 corresponding element of Amia in displaying a conspicuous 

 median ridge, which looks like a distinct bone thrust into a 

 cleft. 



Jaws, Facial and Opercular Bones. 



The hyomandibular is preserved on both sides, and one 

 specimen is shown of two fifths the natural size from the 

 inner aspect in PI. XI. fig. 1. The bone is slightly more 

 than twice as deep as its maximum width measured at the 

 process [p.) for the support of the operculum; it is much 

 laterally compressed, strengthened by a median longitudinal 

 thickening, and by another extending from this along the 

 base of the opercular process. The upper end was evidently 

 capped with cartilage; the anterior margin, completely 

 preserved in the fossil, is gently excavated, and below the 

 opercular process behind there seems to have been an ex- 



