460 



CONTRIBUTION TO THE 



ence to order, sub-class, or class. The fins in their position and attachments exhibit the most remote separation 

 from their characters in the Oroaopterygidm. The base of the cranium is complex, and removed in construction from 

 the simple parasphenoid floor of the lower divisions. The pharyngeal hones are more specially developed than in any 

 other order. The elements of the support of the caudal fin are more thoroughly coossified than in any other except 

 Seombridie and the PleetognatM. 



GENERAL OBSERVATIONS. 



In tracing the affinities of the Phy«ottom% I have pointed out the relation between the Ohondrostei and tho 

 Nematognafhi, and the HaleeomorpM and the l'sospondyli. The series commenoed with the cat-fishes may bo continued 

 into the Mormyri and then to the families of the Plectospondyli, where the series with altered vertebrae and with ossi- 

 culaauditus, terminates. The C'ltaraeins have, however, considerable affinity to the Isospondyli, especially in the type 

 of their branchial bones. From the latter group we pass to the Eaplomi, and thence to the Physoolyst groups, 'flu: 

 eel- like groups form a special lino. The Qlanencheli have cranial characters of the orders with modified vertebrae, 

 (Wematognathi and Plectospondyli,) with fins of the more typical eels. The latter show a steady approach in some 

 points to the conditions characterizing tho Chondrostei. The loss of the maxillary, of opercular bones, and of 

 pharyngeal elements, reminds one of these, hut in the loss of the promaxillary, and great development of the 

 ethmoid in the Ooloeephali, we have features quite unique. The vertebral position of the scapular arch is tho only 

 shark character they possess : while, on the other hand, the HoUotomi are undoubtedly related to the MattacembeluB, 

 a real Physoclytt with spinous dorsal fin. These relations axe as yet entirely inexplicable. 



The affinities among Phywelysti are more clear. Omitting the genus above mentioned, we find the four orders 

 with ventral fins to form a true: series, with a, Synenlognath variation, terminating in the greatly degraded order of 

 Lophobranchii. The Pereesoces give us our nearest connection with the groups with ventral abdominals, and lead atonoe 

 to the Pereomorphi. Prom this centre radiate many lines of affinity. One leads from the Qhaetodontid® through the 

 Aeroneurida to the PleetognatM by the similarity in tho arrangement of the, posttemporal and forms of the, pharyn- 

 geal apparatus. An important division of the Pereomorphi has the basis cranii simple and the branchial arches 

 reduced above, viz : the, Sayphobranchii. The Cottidm are the most generalized family of tho group, and lead on the 

 one hand, to the Triglidos of the Distegi, with which they are generally arranged,— and on the other, to the Blenniidce. 

 Some of the latter elongate the, basal pectoral bones considerably, and lead to tho Batrachidm on the one side, where 

 tho number of those bones is increased, and on tho other to the Pediculati, where the number is diminished. To 

 these groups the Anaeanthini and lleteronomatii are also allied. 



The third upper pharyngeal bone has already presented an increase of mass and use in tho first orders of Physo- 

 clysti with the ventral fins. Among the Pereomorphi, the same increase makes its appearance by little beginnings 

 in some Sciaenidce. It is quite noteworthy in most of tho Oarangidm, a group whose separation from the SeombridcB 

 by Gill, is supported by this part of their organism. Through forms not now specified, approach to the Pharyn- 

 gognathi is made. Here the pharyngeals are modified into a mill-like struoture, which is least specialized in the 

 Embiotoeidce, and most so in the Searvlm. 



Names ok the Orders. 



Of the orders here proposed or adopted, a number have been employed in various senses by ichthyologists. I 

 refer only to those who have defined their groups, as those who have merely given names cannot be understood as 

 authors of anything but those names. A definite idea, of the definition of a group involves tho ability to characterize 

 it, and by such process only can tho idea entertained by the author of a division be determined by others. 



The order NematognatM was named and defined by Prof. Gill in 1801 ;* Prof. Agasgiz has expressed his belief 

 that the order was well established. Additions to its characters are now made. The Synentognathi was also proposed 

 in 1 S09-) as distinct from tho Pharyngognathi, with which J. Miiller had united it. The order of Lophobranehii is 



* Proceed, Arad. Nat. Sciences, Philadelphia, in a "Catalogue of the Fishes of the Eastern Coast of North America." 

 1 Loc. Clt. p. 148. 



