Teeth sharp in the male?, blunt in the female: skin rough; studded with large osseous tubercles terminating in strong spines; one, three, or five, rows of such tubercles on the tail.
R. clavata, Linn. Syst. Nat. torn. i. p. 397. R. Rubus, Bloch, Ichth. pl. 84. (Male). R. clavata, Id. pl. 83. (Female). R. clavata, Don. Brit. Fish. vol. ii. pl. 26. Turt. Brit. Faun. p. 111. Mont. in Wern. Mem. vol. ii. p. 416. Flem. Brit. An. p. 170. Blainv. Faun. Franc, p. 33. Thorn-Back, Penn. Brit. Zool. vol. iii. p. 93. pls. 11, and 12. Id. (Edit. 1812). vol. iii. p. 122. pls. 13, and 14. La Raie bouclee, Cuv. Reg. An. torn. It p. 398.
From two to three feet; sometimes more.
(Form). General form resembling that of the R. macu-lata: snout short, and rather obtuse: mouth wide, transverse: teeth larger than in the above species, and not so closely compacted; set in oblique rows; each with a broad round head, terminating, in the male f, in a strong curved point; in the female, all blunt, with scarcely any trace of a point or cutting edge: nostrils, eyes, and spiracles, much as in the R. maculata: body rather thick, convex above; the whole of the upper surface extremely rough with minute hooked spines and asperities, besides which are a greater or less number of large osseous tubercles, each terminating upwards in a strong hooked spine, or tooth-like process, very sharp at the extremity; these spinous tubercles, which are of an oval form, and very broad at the base, are scattered about in rather an irregular manner, and very variable in number; almost always one or two above the eyes, and a row down the middle of the back, continued along the ridge of the tail; also one or two on each side of the dorsal series about the middle; sometimes three complete rows on the back, and three or five on the tail; occasionally, especially in large fish, the under surface of the body is studded with tubercles as well as the upper; more rarely the tubercles are almost wanting altogether: tail a little longer than the body, depressed, rather stout, and very rough with minute asperities independently of the spinous tubercles; two finlets near its extremity, much as in R. maculata, besides the rudiment of a caudal: pectorals and vent-rals the same as in that species. (Colours). Variable: generally bluish gray above, tinged with reddish brown; the whole sparingly sprinkled with large, but ill-defined, whitish spots: beneath white. A variety sometimes occurs, shewing more or less appearance of an ocellated spot on the middle of each pectoral.
Common as this species is on all parts of the coast, its true characters, at least those which distinguish the sexes, are involved in a little obscurity. Montagu was led to regard the R. Rubus of authors, in which the teeth are sharp, as the male of R. clavata, in which they are blunt, from the circumstance of his not being able to discover a female of the former, nor a male of the latter, species. As far as my own observation goes, which, however, has been but limited, it confirms Montagu's opinion. I have never seen a male Thorn-Back with blunt teeth, but I have seen, in the collection of Mr. Yarrell, two fish perfectly similar in every respect, excepting that in one, a male with long ventral appendages, the teeth were sharp, in the other, a female, the teeth were blunt. These I was led to regard as the sexes of the common Thorn-Back. Yet both Risso and Blainville speak of the sexes of the R. clavata, without any allusion to the teeth being otherwise than blunt, in the male, as well as in the female. Moreover, they both give the R. Rubus as a distinct species. Further observation is necessary in order to clear up this difficulty. According to Pennant, the Thorn-Back preys on all sorts of flat fish, as well as on Herrings and Sand-eels, of which it is said to be particularly fond; also on crabs. Produces its young in July and August, which, until a certain age, are called, in common with the young of the R. Batis, by the name of Maids. It is taken in large quantities for the table.