416 APPENDIX. No. IV. 



April and twentietli of May, and were not seen afterwards, although 

 the preceeding sort were still abundant. 



Gen. II. Alimax Thorax elongate vnXh the sides not approximating. Mouth 

 placed towards the hinder part of the thorax. 



Sp. 1 . AUma hyalina. Occurred abundantly at Porto Praya, and in 7j 37, N. 

 lat. 17, 34, 15 W. long. 

 PnyLLOSoMA,* the most curious genus of Crustacea that has yet been dis- 

 covered, and of which there are at least four very distinct species, occurred 

 in the greatest profusion from the 10th AprU to the 30th May. The shell 

 of this genus is membranaceous and as thin as a leaf; the part containing 

 the mouth, and from whence the legs arise, is drawn backwards and pro- 

 jects beyond the hinder part of the shell. The front of the shell bears the 

 eyes and antennas : the eyes have the first joint of their peduncles very much 

 elongated ; the second joint is short, and the eyes themselves are abruptly 

 larger than their peduncles. The superior aiitemia; are (as in all the other 

 inalacostraca with pedunculated eyes) bifid. The infenor antennfp are vari- 

 able in their projection, and form, affording chai'acters which, for the present, 

 I shall only venture to use for the purpose of specific distinctions. The 

 abdomen has the usual appendages beneath, and those of the last joint are 

 converted into swimming or rather steering lamellfe. The mouth, when first 

 viewed, appears to be trilobate ; this arises from a clypeus similar to that 

 covering the mouth of Squ'dla, and the prominence of the exterior sides of 

 the mandibles, which are much curved and dilated towards their middle ; 

 their points are bifid, and one lacinia is unidentate within. Two pairs of 

 maxiUae are very distinctly to be seen ; the outer ones are terminated by 

 three spines. I have not had time to ascertain the modification of the 

 interior ones, nor to ascertain the existence and insertion of the palpi. The 

 front pair of legs is extremely short and dilated at its base, with all the 

 joints (the first excepted .') confluent. The second pair is short ; the third 

 joint at its base has a flagrum which is articulated towards its point ; the 

 last joint is terminated by long spines and a claw ynih unequal spines. Ihe 

 five foUomng pairs of legs are very long, and the hinder ones gradually 



* The third, fourth, fifth, sixth, and seventli pairs of legs, in the numerous speci- 

 mens sent home, were for the most part broken off at their third joint, the fiagrum only 

 remaining. See the plate. 



