108 



Tadle of Arrangemext.- 



-FISHES.- 



- Dermopteues. 



In the ensuing pages the Primary Groups of Fishes 

 will be ranjred in the folluwlnfr orders : — 



I. 



TABLE OF ARRANGEMENT. 

 — Dekmopteues (Owen), equivalent to Hie 



11. 



OnnER. 

 Myzontes of Agassiz, who considers them to hold the 

 rank of a Class in the Vertebral Branch of Animals. 

 Suborder A. — Pharyngohranclis or Cln-hostomcs, 

 represented only by the Lancelets, which Ag:assiz 

 surmises to be merely embryos of more highly 

 organized fishes. 



Suh order B. — Marsipd)ranc!is (sacculated gilli^), or 

 Cydostomes (round mouths), called also SucJc^rs. 



The next four orders belong to the Fishes proper of 

 Agassiz, and are considered by him to constitute a class, 

 divisible into Ctcnoids s^nd Cycloids: — 



Order. — Anacakths (no spinous fin-rays) having shut 

 swim-bladders, and no radiated or fusiform bone cor- 

 puscles in their skeletons. 



/Suh order A. — Udmiclithynns or Taj^e-Jishcs of 

 Kblliker. 

 " £. — Apodal Anacantlts. 



" C. — Thoracic Anacanths. 



" D. — Uetcrosomcs (Bonaparte), Dissimilar 



sides, or Flat-Iish. 

 ** -E". — Colacides, Parasites or Ship-stayers. 



III. Order. — Pharyngognaths, whose right and left inferior 



))haryngeal bones are confluent, forming one piece. 

 Their skeletons are destitute of bone corpuscles. 

 Sab order A. — Malacopterygian PharyngogimtJis. 

 " B. — Acanthoptcryjian Plmryngognaths. 



IV. Order. — Acantiiopteres, with ossified eudo-skeletons 



without bone-corpuscles; one or more anterior rays of 

 the fins, especially of the ventrals, unjointed or inflexible 

 spines. Ventrals more generally situated in the thoracic 

 or guttural regions ; swim-bladders closed. 

 Sub-order A.~ Ctenoids (Owen). 



*' B. — Ci/doids (Owen), Scomberoid- scaled 



fishes. 



V. MAEACOPTERESorPnY90STOME9,have open air-bladders, 

 flexible, articulated fin-rays, and most generally true 

 bony structure in their skeletons. 



Suh order A. — Apodal Malacopteres, or Scrpentifurm 



Apodals. 

 " B. — Abdominal Malacopteres. 



The Ganoids, as an order of vertebrals in the usual 

 acceptation of tlie name, consist mostly of palfeozoic 

 fishes, and have comparatively few existing representa- 

 tives. Professor Owen enumerates their essential char- 

 acters, as they appear in fossil remains, in these words: 

 '' Endo-skeleton in some osseous, in some cartilaginous, 

 in .some partly osseous, partly cartilaginous; exo-skcleton 

 formed by enamelled bones; fins usually with the first 

 ray a strong sjjine." 



Agassiz ranks them as the third class of vertebrals, 

 and includes in the class the six following orders, but 

 the first three merely provisionally, and dependent on 

 further investigation for their true i>osition in his system. 



VI. Order. — Siluroids (Agassiz). 

 VII. Order. — Lophobranchs, or fishes with tufted gills. 

 VIII. Order. — Plectognatiis, named from the confluence or 

 union by indented suture, of the right and left halves 

 of the upper-jaw and mandible resjiectively. 



This structure of the jaws is not, however, altogether 

 confined to this order. 



IX. Order. — Acipenseroids, or Sturioxidans. 



X. Order. — Sauroids (Agassiz), or Lizard-Fishes. 



XI. Order.— CffiLACANTHs (Agassiz), or Hollow Spines. 



A palaeozoic order which became extinct before the 



tertiary epoch. The dermal spines were ossified only 



externally, and are found hollow in the fossil state. 



The vertebral column ends in a prolonged appendage 



which separates the upper caudal lobe from the under 



one, as in some few existing fishes. 



The fourth class of Vertebrals, according to Agassiz, 



is composed of Kelachians, a term which is equivalent 



to that of Plagiostomes (oblique mouths) of Dumeril, 



It embraces the three succeeding orders: — 



XII. Order. — Holocephalids or Chim-^ekje of Agassiz, 



XIII. Order. — Galeodes or Sharks of Agassiz. [Sipuali or 



Ilaijisdie of Miiller and Henle.) 



XIV. Order. — Batides (Agassiz), Bays and Sicatcs of other 



ichthyologists. Eaim or Bochen of Miiller and llenle. 



XV. Order. — Protopteres of Owen, an osculant form 

 between Fishes and Keptiles, considered by sf^me 

 zoologists to be Amphibians, ildithyodi of Agassiz. J 



Order I.— DERMOPTERES. 



Paleontologists have by successive discoveries car- 

 ried back the first appearance of Fishes to an early 

 period in tlie formation of the crust of the earth ; and 

 Professor Agassiz is of opinion, that it would not be 

 difBoult to sliow on pliysiological grounds, that tlieir 

 presence in primaeval oceans dates contemporaneously 

 with that of the Radiata, Mollusca, and Articulata ; 

 the plan of structure and means of subsistence of tliese 

 tlu'ee great types of the animal kingdom, constituting 

 with the Vertebrals a mutually dependent system. 

 There is, however, as yet no unequivocal evidence of 

 fossil fishes below the newer silurian beds. The earliest 

 remains of fishes have an embryonic character in the 

 position of the mouth on the ventral aspect of the 

 bead, in the beterocercal caudal fin, in the absence of 

 a hard internal skeleton, and in other parts of structure, 

 which, as far as they can be made out, seem not to 

 have been so highly developed as in the modern osseous 

 fishes. The Dermopteres have a more decidedly em- 

 bryonic aspect than any of the other existing groups of 

 fishes. Ko remains of them have been identified in 



the palreozoic strata, either because they were not early 

 creations, or because the softness of their textures mili- 

 tated against tlieir preservation, so as to be recognizable 

 in indurated deposits that have been subjected to the 

 action of heat, great pressure, and sundry displace- 

 ments. Ichthyologists now concur in ranking this order 

 at the bottom of the scale of fishes, and consequently, 

 as the lowest of the vertebrals ; but though in common 

 parlance the Dermopteres are said to be comparatively 

 feebly organized, they are not imperfect, being in every 

 way adapted to fill their station in nature, and to per- 

 form their allotted functions. 



The essential characters of the group, as drawn by 

 eminent zoologists, are the want of the lateral pairs 

 of fins representing hands and feet, that is, they are 

 abrachial and apodal, with long vermiform bodies ; 

 their internal skeleton is not ossified, being either 

 cartilaginous, or merely membranous: their external 

 skeleton does not take even the consistency of scales, but 

 remains in the condition of soft, mueiferous skin ; and 

 the fin-rays and teeth when nrosent are muco-dermoid 



