164 M. Hesse on new or rare Crustacea 



wards. M. Hesse thinlcs that the membranous expansions may 

 also assist in locomotion ; they are moved in the manner of the 

 wings of a buttei-fly. They are probably employed as a point of 

 support and traction, by being applied hermetically, and by pro- 

 jecting, upon surfaces to which the animals wish to adhere, the 

 lobes by which they are accompanied. There is also a very fre- 

 quent and active movement of the mandibles, which might lead 

 to the supposition that these parasites are rather masticators 

 than suckers. 



The young animal, at the second or third transformation, has 

 a nearly uniformly cylindrical body, diminishing gradually, how- 

 ever, towards the posterior extremity, by which it acquires the 

 appearance of a Cyclops. There is as yet no dorsal appendage ; 

 but the last thoracic segment has commenced the modification 

 which fits it for the reception of the ova. The other appendages, 

 although imperfectly formed, resemble those of the adult. The 

 body is hyaline, with the eye alone red. 



Genus Pleurocrypta, gen. nov. 



M. Hesse, in September 1864, discovered under the arch of 

 the branchial cavity of Galatea squamosa a parasitic Crustacean 

 belonging to the group of the Isopoda, which he regards as 

 forming the type of a new genus intermediate between Gyges 

 and Phryocus. He gives the following characters of this para- 

 site, for which he proposes the name of 



Pleurocrypta Galatea. 



" Male. Body elongate-ovate, divided into seven nearly equal 

 thoracic segments, of which the first is amalgamated with the 

 head, which is deeply inserted into it ; and the last is attached 

 to the abdomen, which is triangular and of a single piece. Feet 

 terminated by a strong hooked and denticulated claw. 



" Female. Body ovate, symmetrical, provided above with very 

 long incubatory laminse, which entirely cover the thoracic por- 

 tion ; abdomen divided into six [five ?] segments, furnished with 

 simple acuminate branchise of unequal size ; feet terminated by 

 an oblique, ampuUiform joint, having a prehensile orifice. 



" Length of the male O'OOl, of the female 0-007 m." 



The head of the male is amalgamated with the first thoracic 

 segment, forming a sort of buckler, rounded in front and hemi- 

 spherical above ; the six following thoracic segments are of nearly 

 equal width, but the sixth is a little narrower and soldered to the 

 abdomen. The latter is of an elongate triangular form, rounded 

 at the extremity, and presents no trace of segments, unless it be 

 that the lateral margins are slightly undulated. On each side 



