442 THE VOYAGE OF H.M.S. CHALLENGER. 



(2 mm.), and also figures 1 an older specimen, i^th of an inch (4 mm.) long, in 

 which, besides the characteristic absence of the posterior two pairs of pereiopoda, 

 the anterior three pairs, unlike Sergestes, resemble those of Penseus in all three being 

 chelate. 



On PI. LXVII. of this Eeport, fig. 4 represents an animal 7 mm. long (described as 

 Mastigopus spiniventralis, at page 379), that is almost identical in form with that given 

 by Brooks in his fig. 85 above referred to, excepting that neither pair of pereiopoda 

 possesses any trace of a chelate character. Believing this to be a young Sergestes in the 

 Mastigopus stage, I have named it so accordingly, assuming, that as in every specimen 

 analytically examined I found the posterior pair of pereiopoda in a budding condition, 

 but more or less developed, that they were present in this also, although it corresponded 

 closely with Milne-Edwards' description of the genus Acetes in having the pereiopoda 

 filiform and terminated by a single point (sont filiformes et terminees par un article 

 pointu). 2 To see it figured with three pairs of chelate appendages similar to Pen&us, 

 as shown by Professor Brooks in his plates, and confirmed by his description, suggests 

 that the specimens examined were not the young of Acetes. 



I am aware that Professor Milne-Edwards originally described Sergestes as having 

 the pereiopoda filiform and monodactyle, and that we are indebted to Professor Kroyer 

 for first pointing out that two pairs of these appendages terminated in minute chelae, 

 but Kroyer did not make this character a feature of the genus as has been done in this 

 Eeport, inasmuch as several of the species that he has described in his Monograph 

 on this genus have the pereiopoda terminating in a monodactyle extremity, a 

 condition which, throughout this Eeport, I have attributed to the immature stage of 

 Mastigopus. 



So far as my knowledge goes the genus Acetes has never been fully described or 

 noticed at all from independent observation, since it was first published by Professor 

 Milne-Edwards nearly sixty years ago, nor am I aware of any specimens having been 

 observed, excepting those from which Milne-Edwards drew his description, and which are 

 still preserved in the Museum of the Jardin des Plantes at Paris. These type specimens 

 are recorded as inhabiting the Ganges, in which river, or in the sea near its mouth, they 

 must be very abundant, for among the specimens of Crustacea collected by Sir Walter 

 Elliot, S. I., there were several specimens of Acetes indicus (PI. LXXXV. fig. 1), and 

 with them was a note stating that they were taken in 1852 from a large fish "21 feet 

 in length and 25 broad" (Dicerobates eroogoodoo); its stomach was filled with myriads 

 of these little Crustaceans, which were carried away in bucketfuls by the fishermen, and 

 thousands were left scattered about the shore. 



Milne-Edwards says this genus ought to be placed very near the Schizopoda. 



: Loc. cit., pi. xi. fig. 90. 



1 Ann. d. Sci. Nat., t. six. p. 350, 1830. 



