PARASITIC COPEPODS — WILSON 543 



Remarks. — A commensal harpacticl has been taken from the 

 branchial chamber of a land crab in Jamaica and the curious form 

 Balaenophilus has been found upon the baleen plates inside the mouth 

 of the great blue whale. This is the first harpactid to be obtained from 

 the outside surface of any host. The hard chitin shell of the lobster, 

 however, offers a serious obstacle to true parasitism. Like Balaeno- 

 philus it is probably to be regarded as a commensal profiting by the 

 well-known scavenger habits of its host. 



Suborder Cylcopoida 



Family ERGASILIDAE 



OSTRINCOLA, new genus 



Head fused with the first segment ; segments 2 to 5 of varying lengths 

 but diminishing regularly in width. Genital segment longer than 

 wide with convex lateral margins in the female and parallel margins 

 in the male. Abdomen 3-segmented in the female, 2-segmented in 

 the male ; caudal rami much elongated and cylindrical. 



First antennae 8-segmented in the female, the six distal segments 

 much shorter than the two basal, 8-segmented also in the male but the 

 segments more nearly equal. Second antennae uniramose and 4-seg- 

 mented, the end segment a curved claw. First four pairs of legs bi- 

 ramose, rami 3-segmented, fifth pair uniramose. 3-segmented, the end 

 segment enlarged into a circular disk in the female. 



Genotype. — Ostrincola gr'aeilis, new species. 



OSTRINCOLA GRACILIS, new species 



Plate 34, Figures 219-227 



Four females and three males were taken from the mantle cavity 

 of the common oyster {Ostrea virghvica) at Beaufort, N. C, by H. J. 

 MacDonald in August 1929. One female and one male are designated 

 as holotype and allotype, respectively, of the new species, U.S.N.M. 

 No. 79697. 



Female. — Head fused with the first segment into an acorn-shaped 

 cephalothorax as wide as long. Second segment as wide as the cephalo- 

 thorax, the following segments diminishing regularly in width, the 

 fourth segment with slightly projecting posterior corners, the third 

 and fifth segments longer than the second and fourth. Genital seg- 

 ment subcordate, a little longer than wide, and narrowed posteriorly. 

 Abdomen 3-segmented, the segments diminishing in length and width 

 posteriorly, the anal segment a third as long as the basal and half as 

 wide. Caudal rami cylindrical, very narrow, and four times as long 

 as the anal segment, each tipped with three minute setae. 



