Correspondence. 



271 



one can donbt that a fish may legitimately be compared with a fish, 

 and every one will I think see that there is no effort of the imaginati- 

 on at work, when a Silurus is compared with a Chiloscyllium, a Cobites 

 with Cyclostomous fishes, or some of the mailed Esocidse with the Lo- 

 phobranchse. The Clupeidae represent the Ostinopterygii typically in 

 form, so that I have no doubt you will discover the analogy, as yet 

 unknown to me, which exists between the Salmonidse and Sturiones. 

 I was ignorant of the true arrangement of Cyprinidse until I read your 

 valuable Monograph. I have now no doubt of its being nearly as fol- 

 lows into genera or rather into families : — 



VEILE. MClil. 



Body regular. -^ 



APALOPTERINjE 



M'Clel. 

 Body invested with 

 a slimy mucus. 



f \. PjEONOMJNE, Intestinal canal long ; repre- 

 /. M. senting STURIONES. 



or genus Cypri- 



NUS, L. 



2. SARCOBORI- 

 N,E, J. M. 



or genus Leuciscus, 

 Kl. 



3. P^ECELIANiE, Snout prolonged, no cirri, 



Intestinal canal short ; re- 

 presenting OSTINOPTE- 

 RYGII. 



/. M. 



Or GENUS PjECILIA, 



Sch. 

 4. COBITINjE, 



Branchial rays more than 



three ; representing LO- 



PHOBRANCHII. 



Mouth provided with cirri # 



^ Branchial rays three, CY- 



CLOSTOMI. 

 5. PLATYCARINiE, Head flattened, round, and 

 J. M. short. No cirri, branchial 



or genus Platy- rays less than three ; repre- 



cara, J. M. senting PLAGOISTOMI. 



Thus we see why the Platicaria has the form of a shark ? Why Loach- 

 es, such as Schistura, J. M. have an analogy to the Lampreys and My- 

 xines ? Why Psilorhynchus has so long a snout ? And why Gonorhynchus 

 has the muzzle of a Sturgeon. The nearer two groups are in general 

 structure, the more striking their parallel analogies will be ; and there- 

 fore I think, that by comparing fish with fish, we may obtain more 

 striking analogies than by comparing them, as Swainson does, with 

 mammalia, birds, or insects. At all events, we shall have less reason 

 to distrust the effects of a fertile imagination. Still I am far from 

 denying, that such analogies as he delights in exist in nature. I only 

 say, that they are dangerous things to deal with, and that in his 

 hands, they often become far-fetched and even ludicrous. The cause 



