LEPEOPHTHEIKUS PECTORALIS. 65 



length of the animal. Frontal plates of moderate size, 

 lunulae wanting. Free thoracic segment small. Genital 

 segment subquadriform and equal to about one-third 

 of the entire length of the animal, with its postero- 

 lateral angles rounded. Abdomen short, with a slight 

 constriction near the middle which in certain posi- 

 tions gives it the appearance of being obscurely two- 

 segmented. Caudal rami very short. 



Antennules of moderate size. Antennas armed with 

 strong, terminal, hooked claws. Mandibles small, 

 slender, and with the inner edge of the distal joint 

 distinctly serrated. Posterior maxillipeds strong and 

 provided with stout terminal claws. Sternal fork 

 moderately stout, with short and scarcely divergent 

 rami, each ramus somewhat expanded in the middle 

 and thence tapering to the pointed extremity. Fourth 

 pair of thoracic legs short ; the basal joint tolerably 

 stout, and the rainus consisting of two subequal joints 

 the first with a small spine on the outer distal angle, 

 and the second with three short terminal spines, each 

 of the two inner spines being rather longer than the 

 one in front of it. The fifth pair extremely small and 

 situated near the postero-lateral angles of the genital 

 segment. Length about 5 mm. 



Male. The male is little more than half the size of the 

 female, but the carapace is proportionally larger, being- 

 equal to nearly two-thirds of the entire length of the 

 animal. Genital segment small ; abdomen also small 

 and uniarticulate. 



Habitat. Found usually adhering to the underside 

 of the pectoral fins of certain flat fishes, as plaice, Pleu- 

 ronectes platessa, dabs, Pleuronectes limanda, and one 

 or two others. Belfast (W. Thompson). Plymouth 

 (Sassett- Smith). Irish Sea (A. Scott). Firths of 

 Forth and Clyde (T. Scott). 



This is one of the more common and easily recognized of 

 the species of Lepeophtheirus, but though widely dispersed in 

 the seas of Europe it does not appear to have yet been 

 recorded from American waters. 



VOL. I. 5 



