REPORT ON THE CRUSTACEA MACRURA. 703 



and terminating in a brush of ciliated hairs. The second pair of pereiopoda is longer 

 and more slender than the first, the carpos being narrow and cylindrical, while the 

 propodos and dactylos resemble those of the first pair. The posterior three pairs are 

 slender and nearly of the same length and proportion. 

 The pleon resembles that of Palwmon. 



Observations. — There is but one specimen of this genus in the Challenger collection, and 

 since it was preserved in the same bottle with Atya sulcatipes and two specimens of Atya 

 serrata, it seems almost certain that all these specimens were taken from the same river 

 in the Cape Verde Islands, for I assume from the known carefulness of the collectors that 

 they would have otherwise been separated and labelled accordingly. My first opinion was 

 that the three were successive stages in the growth of one species. But in the examina- 

 tion of a large number of specimens from Honolulu of the closely allied form Atya 

 (Atyoida) bisulcata I found a few with ova, and in some of these the embryo so far 

 advanced that by extracting it from the egg I was enabled to determine that the 

 brephalos is a Zoea (p. 692). 



This at all events settles that the Atyoida form could not be a stage in the growth 

 of Atya, and the fact that several species of Caridina have been found in various 

 localities, in few of which Atya has been recorded, makes one hesitate with our present 

 experience to determine the true relationship, although it is clear that Atya must pass 

 through some such form as Caridina before it can attain its full development. 



The form which Milne-Edwards, under the name of Caridina typus, has described 

 as a genus distinct from Atya, chiefly differs both from that genus and from Atyoida, 

 according to its author, in the third pair of pereiopoda being slender and the second 

 pair having the carpos of the ordinary form. 



The portion of a specimen figured on PL CXIX. fig. 3, appears to me to belong 

 to the same species as that which Milne-Edwards has figured and described under 

 the above name, and it is not improbable that Mdne-Edwards' specimen may have 

 come from the same locality. 



The fragment consists of the pereion with its appendages, and those that belong to 

 the mouth. It is part of an animal still young, but approaching the adult condition, 

 a circumstance that inclined me to believe it to be an immature stage in the develop- 

 ment of Atya, with which it was found associated. Mdne-Edwards' specimen is only 

 ten lines long, and this is probably about the length of the animal to which our 

 fragment belonged. 



The difficulty depends on the singular variation between the form of the carpos 

 in the first two pairs of pereiopoda. In the adult Atya the carpos of both pairs is 

 short, robust and lunate, but in Caridina the carpos in the first pair corresponds 

 with that of the adult Atya, while in the second pair it is long, slender and cylindrical. 



