20cS 



Part III. — Eleventh Annual Report 



Posterior antennae four-jointed, joints subequal in length, but the last 

 two are more slender than the first and second : the apex is furnished 

 with three claw-like and hooked spines, and also a seta of about the same 

 length as the spines. Mandibles nearly as in Lichomolgus forficula, 

 Thorell. Basal part of the anterior foot-jaws stout, terminal part ex- 

 tremely long and slender, gradually tapering to a setiform extremity, and 

 bent at nearly right angles to the basal part ; the upper edge of the ter- 

 minal part is furnished with a fringe of cilia which extend from the geni- 

 culation, where they are stout and setiform, but rapidly decrease in size 

 towards the extremity. Posterior footjaws in the female rudimentary, 

 three-jointed, the last very small, and without any spines or setae ; the 

 posterior foot-jaws in the male form powerful grasping organs, composed 

 of two stout joints, and a very long falciform terminal claw, which carries 

 a small seta at its base ; the second joint has the distal half of the inner 

 edge fringed with cilia (fig. 19). Both branches of the first four pairs of 

 swimming feet three-jointed, and of nearly equal length ; the first basal 

 joint of the first pair is furnished interiorly with an elongate and stout 

 plumose seta, the inner margins of both branches are also provided with 

 long plumose setae ; the armature of the inner branch comprises one seta 

 on the distal end of the inner margin of the first joint, two on the second, 

 and two on the third joint ; there are also four short dagger-shaped spines 

 round the end of the third joint, and the outer distal angles of the first 

 and second joints form tooth-like processes : there is no seta on the inner 

 edge of the first joint of the outer branch, one on the second and five on 

 the third joint ; the third joint is also armed on the outer margin and 

 end with four dagger-shaped spines — the terminal one being the largest ; 

 the second also bears one dagger-shaped spine on the outer distal angle, 

 and the first joint one. The armature of the fourth pair differs from that 

 of the first in the following manner — there is no seta on the interior edge 

 of the second basal joint, the first and second joints of the inner branch 

 bear each a long plumose seta on the distal end of the inner margin, there 

 is no seta on the third joint ; this joint is truncate at the end, and armed 

 with two stout dagger-shaped terminal spines ; the outer distal angle of 

 the second joint forms a bifid toothed process, and there is a small tooth 

 on distal end of the outer margin of the first joint ; the second joint of 

 the outer branch bears one long seta on the inner margin, and the third 

 joint five seta ; the third joint is also armed at the extremity with a long 

 sabre-like spine, ciliate along the inner edge, and with two short dagger- 

 like spines on the outer margin ; and the first and second joints are each 

 provided with a similar spine on the outer distal angle (fig. 21). The 

 fifth pair are small and one-jointed, the apex truncate, and furnished 

 with one long, stout, and slightly curved spine, and a small spiniform 

 seta, both of which are plain (fig. 22), fifth pair alike in both sexes. 

 First abdominal segment in both sexes considerably dilated ; that of the 

 female has the sides rounded, is widest across the middle, and furnished 

 on each side, on the ventral aspect, with a small setiferous appendage ; 

 that of the male is widest across the distal end, the distal angles are 

 somewhat produced, and provided with three small setae. The second, 

 third, and fourth abdominal segments have the posterior margins in both 

 sexes strongly setose. Caudal stylets about equal to twice the length of 

 the last abdominal segment, and furnished with a small seta on the 

 proximal half of the outer margin, and with four apical setae ; the male 

 abdomen is rather smaller than that of the female. Ovisacs two, large. 

 Colour of the animal, including ovisacs, usually brilliant red. 



Habitat. — Living as a messmate within the shell of the ' horse mussel,' 

 Mytilus modiolus. Frequent in the Firth of Forth. I have also obtained 

 Modiolicola in Mytilus modiolus, both in the Moray Firth, on the East 



