CAUDAL FIN. 33 



the external ones^ so that they form a lobe on each of 

 their sides — one above^ the other below. Where such 

 numerous gradations occur, it is impossible to define with 

 strictness the limits of our definitions ; we may, never- 

 theless, arrive at some degree of precision, by con- 

 sidering each of these forms as presenting the follawing 

 modifications : — A rounded fin is either lanceolate, oval 

 round, even, or truncate. On reaching this latter, we 

 may draw an imaginary line, and enter upon the fork- 

 tailed division. Truncate fins pass into those which 

 are slightly crescent-shaped ; they next become lunate, 

 forked, lobed, and, finally, emarginate; while these latter, 

 again, pass into rounded fins : the highest development 

 of each of these is seen in the lanceolate and the forked ; 

 the other modifications gradually recede from each other. 

 (35.) We shall now endeavour to define each of these 

 forms. — 1. Lanceolate, &o named from the shape bearing a 

 resemblance to the head of a lance : the longest ray is in 

 the centre, and stands singly ; all the others are in pairs, 

 diminishing, more or less gradually, in length, until 

 those that are external become the shortest. Nearly 

 all the species of Cepola [fig. 3. a) possess this character, 

 but it is by no means frequent, and is chiefly seen 

 in that genus, Gobius, and in Scicena pama (Cuv. 

 pi. 101.). — 2. Ohlong oval: not quite so long in pro- 

 portion as the last ; the middle is not pointed, and 

 the shape is that of the smaller end of an egg. 

 This form may be called a highly developed state of 

 the next, and is confined to few examples. — 3. Round : 

 the fin is of moderate size, always shorter than the last, 

 and the extremity describes the segment of a circle. 

 This is the most common shape in this division, and 

 per^'ades all the flat fish (Pleuronectidce), a few of the 

 rocklings (Motella Cuv.), all the gobies (^GoUadce), the 

 goius Syngnathus, &c., none of which are capable of 

 long sustained swimming : the degree of roundness 

 varies ; but we still retain the name to all such fins as 

 have the central rays in any degree longer than those 

 on their sides. — 4. Even : the majority of the rays are 



VOL. I. D 



