— 144 — 



lateral edge of the parieto-extrascapular, that bone not overJapping the suprascapular at all. The 

 remainder of the anterior edge of the bone suturates with the lateral extrascapular and pterotic. 

 The bone is traversed by the main infraorbital latero-sensory canal and lodges one organ of that 

 canal. The canal leaves the bone by a large opening on its lateral edge, near its bind end, and immed- 

 iately anterior to this opening, on the ventral surface of the bone, the wide stout opisthotic process 

 arises. Immediately postero-mesial and also immediately postero-lateral, to the bind edge of the 

 base of the opisthotic process, there are small articular facets. These two facets give articulation to 

 two articular eminences on the dorsal edge of the supraclavicular, these eminences embraeing the 

 bind edge of the opisthotic process of the suprascapular. From the deep layers of the bind edge of 

 the epiotic region of the bone there projects postero-mesially a thick plate of bone which gives support, 

 on its dorsal surface, to the first one of the series of dorsal plates on the body of the fish. 



The SUPRACLAVICULAR is a somewhat triangulär bone, the external surface of which is 

 slightly concave and partly covered with small granulations. On its short dorsal edge, which repre- 

 sents the base of the triangle, are the two little eminences, above referred to, which articulate with 

 the suprascapular. Posterior to these eminences, the dorso-posterior corner of the bone is traversed 

 by the main latero-sensory canal, and lodges one organ of that canal. The ventral end of the bone is 

 pointed, instead of being expanded as in Trigla, but, as in that fish, it overlaps externally and is 

 bound to the dorsal end of the clavicle; and, excepting that the bone is relatively smaller than in 

 Trigla, there is nothing abnormal in its position or relations to the other bones. 



The PARASPHENOID has the shape shown in the figures. The ascending process of either 

 side rises at about the posterior quarter of the length of the bone, and is a thin triangulär plate that 

 lies transversely to the axis of the bone instead of parallel to that axis. The point of the triangle is 

 directed upward and the base downward, and from this base of the triangle a thin flange of bone 

 extends forward along the lateral surface of the bone. The mesial edge of the triangle is thickened 

 somewhat, is directed dorso-latero-posteriorly and terminates in a sharp point; and this thickened 

 part alone of the triangle would seem to be the homologue of the entire ascending process of the bone 

 in the other fishes so far described, for it alone lies between the anterior edge of the posterior 

 portion of the body of the bone and the bind end of its tbickened interorbital portion. The triangulär 

 plate can accordingly be considered as a thin flange of bone that arises from the lateral surface of the 

 ascending process proper; this flange projecting laterally and slightly posteriorly, and, at the ventral 

 end of the process, being beut forward, in a rounded angle, and then continued forward as a flange 

 that projects laterally and slightly ventrally from the ventral edge of the lateral surface of the inter- 

 orbital portion of the bone. 



On the dorsal surface of the interorbital portion of the parasphenoid, two thin laminae of bone 

 arise, and converging posteriorly, unite, slightly anterior to the ascending processes of the bone, to 

 form a median tooth-like process. The triangulär space between the two laminae lodges, as in Trigla, 

 the ventral end of the cartilage of the interorbital septum, the bind end of the process giving attach- 

 ment to membrane that represents the leg of the basisphenoid; that bone being wanting in Peristedion. 

 On the dorsal surface of the posterior portion of the parasphenoid there is a median longitudinal 

 raised portion which is deeply grooved on its dorsal surface. This raised portion fills the hypophysial 

 fenestra, the groove on its dorsal surface forming part of the floor of the myodome. The hypophysial 

 fenestra extends -backward ^slightly beyond the anterior edge of the basioccipital. 



