PETROMYZON.] PISCES (CARTILAG.) CYCLOSTOMI. 521 



hind, beneath the anterior portion of the second dorsal, and at nearly, 

 but not quite, three-fourths of the entire length : caudal rounded at the 

 extremity, giving a truncated appearance to the tail, the fleshy portion of 

 which, however, is pointed ; underneath, the caudal is continued for a 

 little way towards the vent, sinking gradually into a low ridge represent- 

 ing the anal. (Colours.) Above, greenish or yellowish brown, marbled 

 with dark brown and dusky : beneath, white, tinged with reddish. 



A migratory species, entering rivers from the sea early in the Spring 

 to spawn, and returning after the expiration of a few months. Common 

 in many parts of Great Britain, but said to be more abundant in the 

 Severn than in most other rivers. Attains to the weight of between four 

 and five pounds. Has the power of adhering very firmly to stones with 

 its circular mouth, by means of suction. Flesh much esteemed. Obs. It 

 was formerly supposed that in this and the next species the two sexes 

 were united in the same individual ; this has, however, been since proved 

 to be erroneous *. 



210. P. Jluviatilis, Linn. (River Lamprey.) Dusky 

 blue above, silvery beneath : dorsals widely separate ; the 

 posterior one angular, uniting with the caudal. 



P. fluviatilis, Linn. Syst. Nat. torn. I. p. 394. Block, Ichth. pi. 78. 

 f. 1. Don. Brit. Fish. vol. HI. pi. 54. Turt. Brit. Faun. p. 110. 

 Flem. Brit. An. p. 163. Blainv. Faun. Prang, p. 6. pi. 2. f. 1. 

 Lampetrse medium genus, Will. Hist. Pise. p. 106. tab. G. 3. f. 2. 

 Lesser Lamprey, Penn. Brit. Zool. vol. HI. p. 79. pi. 8. no. 28. 

 Id. (Edit. 1812.) vol. in. p. 106. pi. 10. Bowd. Brit.fr. wat. Fish. 

 Draw. no. 16. Lamproye de riviere, Cuv. Reg. An. torn. n. 

 p. 404. 



LENGTH. From twelve to fifteen inches. 



DESCRIPT. (Form.) General form resembling that of the P. marinus, 

 but more elongated in proportion : anterior half of the body thick and 

 semicylindric ; posterior portion much compressed : mouth similar ; teeth 

 less numerous ; one large tooth above, in the middle, with two remote 

 points ; opposed to it below, a larger one, forming the arc of a circle, with 

 seven or eight points, and having a crenated appearance; a few other 

 smaller teeth at the corners of the mouth : eyes large : nostril single, in 

 the middle of the upper part of the head, a little in advance of the eyes: 

 line of the branchial apertures commencing nearly on a level with the 

 eyes, but inclining a little downwards posteriorly: skin every-where 

 smooth: a considerable space between the two dorsals: the first com- 

 mencing at about, or a very little beyond, the middle of the entire length, 

 low, and nearly of equal height throughout: the second commencing 

 beyond two-thirds of the entire length, low at first, but elevated about 

 the middle into a sharp projecting angle, then again sloping off to meet 

 the caudal with which it unites: vent at exactly three-fourths of the 

 entire length: anal narrow, extending to, and also uniting with, the 

 caudal. (Colours.) Dusky blue above; silvery white beneath: fins 

 whitish. Said, however, by Donovan, to be very variable. 



Common in many of our rivers, especially in the Thames, about Mort- 

 lake, where large quantities are said to be caught annually, and sold 



* See Mr. Yarrell's observations on this subject in the " Proceedings of the Zoological Society," 

 1831. p. 135f. See also some remarks by an anonymous author in Loudon's " Magazine of Natural 

 History," vol. in. p. 478. 



