184 BRITISH PARASITIC COPEPODA. 



respects with that genus, yet differed because of the 

 remarkable arrangement of the cephalic appendages. 

 In typical Chondracanthus these appendages are 

 situated in more . or less proximity to each other, but 

 in Medesicaste the anterior portion of the cephalo- 

 thorax, which has a bulb-like form, and is provided 

 with two pairs of antennae; is separated from the 

 thorax and the thoracic appendages by a moderately 

 long and narrow neck : by this arrangement a con- 

 siderable distance intervenes between the two pairs of 

 antennas and the mouth and other thoracic organs. 

 The posterior part of the body is tolerably large and 

 robust, its lateral margins are deeply incised, dividing 

 it into two portions : the thoracic, which carries on 

 the ventral aspect two pairs of bilobed blunt-pointed 

 processes and other appendages ; and the genital, 

 which is rounded and rather larger than the other, and 

 has its postero-lateral corners produced into more or 

 less angular lobes. Abdomen small, biarticulated, and 

 more or less inclosed between the lateral lobes of the 

 genital segment. Egg-strings elongated, claviform. 



Male very small, similar to the male of Chondra- 

 canihus. 



We are unable to find any valid difference between .1 /r ,/-*/- 

 rrt.v/e Kroyer and Oral i en Bas sett- Smith. 



The only British species of Medesicaste is that described 

 below. 



1. Medesicaste asellinum (Linn.). 

 (Plate LII, fig. 6; Plate LVII, figs. 18, 19.) 



1761. Lernaea asellina Linn. Fauna Snec., 2101 ; Syst, Nat., Edit. 12, 

 vol. i, pt. ii, p. 1093 (1767). 



1829-1843. Chondr acanthus triglse, Guerin-Meneville. (55) Incono- 

 graph., pi. ix, fig. 8. 



1822. Lernentoma triglse Blainv. (24) p. 441, pi. Ixii, fig. 12. 



1832. Chondrocanthus triglse Nordmann. (89) p. 116, pi. ix, figs. 1-4. 



1838. Chondracanthus triglse Kroyer. (70) p. 135, pl.'iii, fig. 3. 



1850. Lernentoma asellina Baird. (4) p. 329, pi. xxxv, fig. 4. 



1863. Medesicaste triglarum Kroyer. (71) p. 312, pi. xviii, fig. 1, a-b. 



1869. Chondracanthus triglx Steenstrup. (126a) pi. ii, fig. 3. 



1896. Chondr acanthus triglx Bassett-Smith. (6) p. 13, pi. iv, fig. 4. 



1899. Oralien asellinus idem. (8) p. 490. 



