The "Cheek-armoured Acanthopterygians," "Joues cuirassées" of Cuvier, after the exclusion of the Sticklebacks, form a perfectly natural association, evidently derived from the Serranidae, with which the more generalised forms have much in common. From the Perch-like genus, Sebastes, a continuous series can be traced towards the Triglidae, especially through such forms as Apistus, Minous, and Choridactylus, in which one or more of the lower pectoral rays are detached from the rest of the fin. Through the Comephoridae the Scorpaenidae are connected with the Cottidae, whilst the latter merge insensibly into the still more aberrant Cyclopteridae. These conclusions, which are apparent enough from a mere comparison of the external characters, become fortified by a study of the skeletons. The passage between the various groups here accepted as families is so complete that no serious objection could be raised to their union in one great family with a number of minor divisions.
Fig. 423.—Left pectoral arch of A, Sebastes percoides; B, Scorpaenichthys marmoratus; C, Dactylopterus volitans. cl, Clavicle; cor, coracoid; pcl, post-clavicle; p.r, pectoral rays; ptr, pterygials; ptte, post-temporal; sc, scapula; scl, supraclavicle.
The character from which the Scleroparei derive their name is subject to many modifications. The second suborbital (the third if the praeorbital be regarded as the first) may be merely enlarged and prolonged over the cheek towards the praeoperculum (Sebastes, Anoplopoma), or firmly ankylosed to the latter (Scorpaena, Platycephalus), or form part of the external armature of the head (Trigla, Dactylopterus). The structure of the base of the pectoral fin appears to afford important characters for the definition of the families, as first pointed out by Gill; these characters have, however, not yet been tested on a sufficient number of the very numerous forms grouped under Cottidae, some of which I have already transferred to the Comephoridae.
Synopsis of the Families.
I. Head not completely cuirassed.
A. Ventral fins not widely separated; none of the pectoral pterygials in contact with the clavicle.
Two nostrils on each side; basis cranii double; gill-membranes free from isthmus .......... 1. Scorpaenidae.
A single nostril on each side; basis cranii double; gill-membranes free from isthmus .......... 2. Hexagrammidae.
Two nostrils on each side; basis cranii simple; gill-membranes free or narrowly attached to isthmus .......... 3. Comephoridae.