1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 583 



" tube rudimentary." This so-called " lube," be it remarked, is a cham- 

 ber for the insertion of the rectus muscles of the eye ; this is isolated 

 from the braiu cavity by the development of a platform from the basi- 

 occipitine continuous with horizontal ridges or shelves diverging from 

 the inner walls of the prootic bones and meeting along the middle, thus 

 constituting a roof for the muscular chamber and a floor for the cranial 

 cavity. This special chamber may be called the myodome.* The cham-. 

 ber, as can be readily seen by bisection of the skull of any Cottid, is too 

 well developed to be called a rudimeutary," and in Scorpasnichthys, also 

 referred to by Professor Cope, it is actually little less it not indeed quite 

 as well developed as in the Scorpcenidce, and does not differ from that of 

 the Trigloidea, and only differs from that of the Seorpcenidw by the trans- 

 verse anterior margin of the shelf and the absence of the diehost or so- 

 called basi-sphenoid bone. We have, in fact, among the mail-cheeked 

 fishes almost all transitions. In the Hexagram midrv or Chiridce the basi- 

 sphenoid bone is almost if not quite as well developed as in the majority 

 of acanthopterygian fishes, and sends down processes to the parasphe- 

 noid. In the Scorpccnidce it is developed mostly as a triangular element 

 in front, and has no descending process, while in the Cotiidce it appears 

 to be entirely absent. In all of these fishes, however, the muscular 

 cavity is differentiated, and the only difference, exclusive of the presence 

 or absence of the diehost or basi-sphenoid, is the relative extension 

 forwards or projection of the roof of the muscular cavity. The principal 

 deviations from the standard occur in the Hemitripterids, the Cyclop- 

 terids, and the Dactylopterids. 



So great is the variation in this group, and so widely do some types 

 deviate from the pattern exhibited by the typical acanthopterygian 

 fishes, that a number of exceptions are manifested by various forms to 

 the characters by which Professor Cope has restricted the major groups 

 including them. This proposition holds true not only as to the subor- 

 dinal or equivalent groups, but as to the orders and even the tribes. 



The tribe of Physoclysti (Pbysoclisti) is defined as having, among 

 other characters, "the parietals entirely separated by the supra-occip- 

 ital." This character, however, is not exemplified by the Hemitripte- 

 rids, Cottids, Triglids, and Peristediids, for in all those families the 

 parietal bones approach and join each other by suture overlapping the 

 supra-occipital. 



The order of Percomorphi is defined as having, among other charac- 

 teristics, the u epiotics normal ; no interclavicles ; post-temporal not co- 

 ossified with the cranium ; basal pectoral radii not enlarged," and u the 

 sub- and inter-operculum present, plate-like." Exceptions occur among 

 the mail-cheeked fishes to each of these generalizations. 



The epiotics can not be said to be normal in such forms as the Agon- 

 ida\ Triglidw, Peristediida>, and Dactylopteridw, in which they are spe- 

 cially modified for union with the supra temporals and otherwise. 





Myodoine : Gr. uva (/ivog), muscle; So/wg, chamber. 



