356 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



A CONTRIBUTION TO THE TERMINOLOGY OF ICHTHYOGRAPHY. 



Br THEODORE CIL,!.. 



A desideratum af ichthyography, or descriptive ichthyology, has been 

 a system of terminology by which the forms characteristic of various 

 types of fishes could be tersely and aptly expressed. In common with 

 others, I have hitherto employed phraseology expressive of likeness to 

 certain specific forms, such as Perciform. Spariform, Scombriform, Cot- 

 tiform, Gadiform, «S:c. But such terms are often taken too literally, 

 or, when e'xplained awaj^, lose almost all significance. When the con- 

 stituents of natural families are compared, however, as Professor Agassiz 

 long ago suggested, * there is generally (not always) found to be a cer- 

 tain similarity which on analysis often proves to be the result of the ex- 

 tension of the body in a definite direction. This tendency can be ex- 

 pressed by terms derived in the same way as many generally accepted 

 ones {€. g., dorsad, caudad, veutrad, &c.) with the suffix form. Some 

 others can be used with current meanings. The advantage of such a 

 course will be (1) to direct immediate attention to the principal element 

 of the form, (2) to dissever the general idea from a special one, and (3) 

 to insure conciseness and absence, or at least a minimum, of periphrasis 

 in description. I shall now give only some illustrations : 



I. 



The form most eminently- adapted for direct horizontal progression in 

 the water is that exemplified in the Tunny and its relations, Trachu- 

 rus, Gasterosteus, t&c. It is the fusiform contour. 



In most fishes there is, however, a greater or less deviation from 

 this form to enable the fish more readily to descend or ascend or other- 

 wise accommodate itself to its most advantageus movements. 



II. 



In most forms extension takes place in an upward direction. In 

 the Perches and many others the tendency of extension is upwards 

 above the shoulders or in the region of the front of the back. This may 

 be called dorsadiform. 



* The idea of taking form as a family cliaracteristic in ichthyology originated with 

 de Blainville in 1816. In the " Squammodermes " or scaly fishes, he defined the 

 families by their form. Metrosomes, "de forme ordinaire" ; Suhencheliosomes, "lougue 

 et subcylindrique ; " Encheliosomes, "lougue et cylindrique," &c. Some of these are 

 repeated under several orders, e. g. : Subencheliosomes under the Tetrapodes Abdom- 

 inaux (CoUtea), T. Thoraciques {Gobies, CaUionymes), T. Jugulaires, and Dipodes 

 (Gymnotes). How little of precision was connected with de Blainville's idea may be 

 inferred from the fact that under Metrosomes he embraced Esox, Chtpea, Sahno, Cypri- 

 nus (Aliilominaux), Labrus (Thoraciques), and Gadus (Jugulaires). 



