ICHTHYOLOGY OF THE LESSER ANTILLES. 



449 



Batrachia and higher classes, the dill'orcnces consisting rather of number and position of parts. The pelvis of the 

 Dipnoi might be regarded as of primary importance but for its existence in tin; Holocephali, whoso limbs again are 

 so near those of the sharks. It remains, therefore, to adopt the Linnaean and Cuvierian class Pisces, and to grawt 

 as sub-classes the groups of Holocephali, Selaohii and Dipnoi. There remain as sub- classes the groups typified by 

 Polypterus on the one hand, and the true fishes on the other. The first has been already distinguished in its external 

 characters by Prof. Huxley, who again brought light out of obscurity when he established "his third sub-order 

 of Ganoids, the Crossopterygidw."* This division is in my estimation a natural one, and to be elevated to a rank 

 equivalent to that of each of the three aboved namod, being the only part of the original division of Ganoids of Agassi z 

 entitled to it. Prof. Huxley defined it as follows : " Dorsal fins two, or if single, multifid or very long ; the 

 pectoral and usually the ventral fins lobate; no branchiostegal rays, but two principal with sometimes lateral and 

 median jugular plates situated between the rami of the mandibles; caudal fin diphyeercal or heterocereal; scales cycloid 

 or rhomboid, smooth or sculptured. ' ' 



Of tho abovo characters, that which relates to the lobate fins is the essential one, and is the expression of the 

 external appearance produced by the structure of the bones of the limbs already pointed out by Gcgenbaur. The 

 dorsal fins of some families it is true, possess a remarkable structure, but in Phaneropleuron, IIuxl. and some others 

 appears to be nearly like that of the Dipnoi. The absence of branchiostegal rays is important, but is shared by 

 tho sturgeons. Tho jugular plates appear to exist in Polypterus only among recent fishes, though several, as Amia, 

 Elopa, Oiteogloetwm, etc., possess a median one. Nevertheless, its nature would not lead one to anticipate its being 

 a constant feature in any group of high rank; at least such is our usual experience with dermal bones. Tho structures 

 of the skin and scales given by Huxley are very subordinate. 



The remaining division answers then to tho Teleostei and Ganoidoa of Midler, minus Polypterus. The name 

 Teleostoi cannot bo preserved for this division owing to its entire want of coincidence with that division of Midler, as 

 well as from the fact that the cartilaginous sturgeons must be included in it. I propose, therefore to call it the 

 Actinopteri.\ The characters of the live sub-classes will then be as follows : 



Class PISCES. 



The hyomandibular bone continuous with tho cartilaginous cranium, with a rudimental opercular bono. Two 

 distinct pelvic bones on each sido. Derivative radii sessile on tho sides of tho basal bones of tho limbs, separated 

 from the articulation. holocephali. 



Hyomandibular bono articulated with the cranium; no opercular pelvic bones. Derivative radii sessile on the 

 sides of the basal bones of the limbs, rarely entering articulation. selacuiii. 



Hyomandibular bone articulated ; rudimental opercular bones. A median pelvic element. Limbs consist- 

 ing of the axial line commencing with the metapterygium and with multiplied axial and often lateral segments. 



DIPNOI. 



Hyomandibular articulated, opercular bones well developed, a single oeratohyal ; no pelvic elements. Limbs 

 Inning derivative radii of the primary scries on the extremity of the basal pieces, which arc in the pectoral, 

 metapterygium, mesoptergium, and propterygium. ohossoptekygia4 • 



Opercular bones well developed on separate and complex suspensorium ; a double oeratohyal, no pelvic elements. 

 Primary radii of fore limb parallel with basilar elements, and entering the articulation with scapular arch. Basilar 

 elements reduced to metapterygium and very rarely mesopterygium. Primary radii of posterior limb generally 

 reduced to one rudiment. actinoptkki. 



The only sub-classes considered here are the last two. 



•See Mem. Geolog, Surrey United Kingdom Decade x. p. 23. 



tFrom axrlf a radlui, and Xrepov fln or wing, from the suppori of the fins by the radial elements only. . 

 t Altered from Huxley's Groaaoptvrygidcit 



AMERT. PHILOSO. SOO. — VOL. XIV. — 118 





