100 BRITISH PARASITIC COPEPODA. 



Genus 17. ORTHAGORISCICOLA Poche, 1902. 



Syn. Laemargus Kroyer. (Name preoccupied for a genus of fishes.) 



Female. Carapace, outline trapezoidal, consider- 

 ably narrower in front, posterior corners rounded, 

 length equal to about three-fourths of the width at 

 the widest part. The first and second thoracic seg- 

 ments very short and fully half as wide as the carapace. 

 Third segment provided with an expanded dorsal 

 plate, which overlaps a considerable portion of the 

 genital segment and is divided posteriorly by a median 

 cleft into two broadly-rounded lobes. Genital segment 

 enlarged, dorsal plates greatly expanded, contiguous, 

 slightly overlapping each other in the median line, 

 and, viewed from the dorsal aspect, entirely concealing 

 the abdomen and caudal rami. 



Antennules tolerably elongated and composed of 

 three joints. Antennas, mandibles, and maxillipeds 

 somewhat similar to those of Philorthragori-scus. All 

 the thoracic legs biramous ; the first and second pairs 

 both somewhat similar to the normal type observed in 

 this group of parasites, but in the third and fourth 

 pairs the rami consist of broad one-jointed laminae 

 almost devoid of spines or seta3. 



Male. The male resembles the female but is 

 rather smaller. The structure of the appendages 

 does not greatly differ except that the antennae and 

 second maxillipeds are armed with stronger terminal 

 claws ; the rami of the third pair of thoracic legs are 

 also biarticulate. 



Kroyer established this genus in 1837 under the name of 

 Lsemarguft, but it happened that only a short time before the 

 same name had been given to a genus of fishes by Henle 

 (1837). 



1. Orthagoriscicola muricata (Kroyer). 

 (Plate XXI, fig. 5; Plate XXVIII, figs. 8-18.) 



1S37. Lxmargua muricatus Kroyer. (70) p. 487, pi. v, figs. A-E. 

 1850. Lxmargus muricatus Baird. (4) p. 295, pi. xxxiv, figs. 3 & 4. 

 1857. L&rnargus muricatus Hoaven. (6la) Op. cit. p. 11, pi. iv, figs. 

 1-10, 12, 14, 15. 



