286 



MR. C. TATE REGAN ON 



[Nov. 4, 



which it so closely I'esembles in other skeletal charactei's, the so- 

 called ribs are epipleurals. 



In the Plectognathi the post-temporal is more reduced and 

 more intimately connected with the skull than in the Acanthurida9, 

 in which family it is attached by its proximal and distal ends, but 

 separated from the skull by a foramen for most of its length. 



The CO- ossification of the pelvic bones is more complete in these 

 fishes than in the Acanthuridse. 



Text-fic-. 56. 



Prajcaudal and anterior caudal vertebras, with epipleurals, of Balistes aculeatus. 



In Dr. Gill's diagnosis of the Plectognathi occtir the words : 

 " The elements of the lower jaw consolidated into two pieces 

 representing the rami ; " this applies very well to the Sclerodermi, 

 but in the Gymnodontes the sutvire between dentary and arti- 

 culare is quite evident, and in Mola at any rate these bones can 

 scarcely be described as consolidated. Another character used by 

 Gill to define the Plectognathi is " Interoperculum detached from 

 the other opercular bones, reduced and more or less rod-like in 

 form." I find that in the Sclerodermi this bone is rod-like 

 anteriorly, and posteriorly expanded and attached to the sub- 

 operculum, this posterior portion being in some cases, e. g. Tria- 

 canthus, strongly ossified, in others, e. g. Osfracion, almost entirely 

 membranous. In the Gymnodontes it is rod-like, but only in the 

 Tetrodontidje is it unconnected postei-iorly with the suboperculum. 



Division I. Sclerodermic 



Supraclavicle vertical ; pterygials (pectoral basalia) not enlarged, 

 movably attached by ligament to the scapula and coracoid, three 

 to the former and one to the latter. All the vertebrae with the 

 neural arches forming a single spine. Basis cranii more or less 

 distinctly double. Dentary and articulare completely co-ossified. 



1 Trachyceplmlus De Vis {nee Tsclmdi), described as a Scleroderm in Proc. Linn. 

 Soc. N.S.W. viii. 1883, p. 455, is evidently not a Plectognath. 



