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. pl. 78. f. 1. Don. Brit. Fish. vol. iii. pl. 54. Turt. Brit. Faun. p. 110. Flem. Brit. An. p. 163. Blainv. Faun. Franc, p. 6. pl. 2. f. 1. Lampetrse medium genus, Will. Hist. Pise. p. 106. tab. G. 3. f. 2. Lesser Lamprey, Penn. Brit. Zool. vol. iii. p. 79. pl. 8. no. 28. Id. (Edit. 1812). vol. iii. p. 106. pl. 10. Bowd. Brit.fr. wat. Fish. Draw. no. 16. Lamproye de riviere, Cuv. Reg. An. torn. ii. p. 404.
From twelve to fifteen inches.
(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 commencing 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 to the Dutch to be used as bait in the Cod-fisheries. Food, according to Bloch, insects, worms, small fish, and the flesh of dead fish. Spawns towards the end of April or beginning of May. Sometimes called a Lampern.
* See Mr. Yarrell's observations on this subject in the " Proceedings of the Zoological Society," 1831. p. 133. See also some remarks by an anonymous author in Loudon's "Magazine of Natural History," vol. iii. p. 478.