III.—Supernumerary Pectoral Fins in Raia circularis Loudon

Abstract

A Male Sandy Ray (Raia circularis Loudon) caught in the North Sea, off Aberdeen, measured 47·5 cm. broad by 43 cm. long (excluding the tail) and exhibited an abnormality which is of very rare occurrence. This consisted of two well-developed fins situated ventrally and associated with the pectoral girdle and the last two branchial arches. The measurements of the fins in the formalin-hardened specimen were as follows: length, 8 cm.; breadth at base, 1·3 cm.; breadth at free end, 2 cm. (left), 3·2 cm. (right); thickness at base, 0·7 cm. The integument covering the lateral and medial borders of the proximal portion of each fin was continuous with that over the fourth and fifth gill clefts respectively. In addition, a strong fold of integument bound the proximal fourth of each fin to the ventral aspect of the body of the fish (fig. 1). A brownishred pigment was present on the ventral aspect of the terminal third of each, and a less marked pigmentation of the same colour on the dorsal aspect of the middle third. Small denticles, similar to those found elsewhere on the fins, were numerous on the distal third, but were more abundant on the dorsal aspect.