760 THE VOYAGE OF H.M.S. CHALLENGEE. 



strong ridge or tubercle on the under surface by which it is retained in position, as 

 in the genus Oplophorus. 



The fingers of the chelae of the first two pairs of pereiopoda are long and slender, 

 while the dactylos of the third and fourth pairs is long and styliform, and that of the 

 fifth pair is short, stout, curved, unguiculate, serrate, and hidden amongst a brush of hairs 

 more or less serrate and one strong spine at the extremity of the propodos. 



The telson (fig. 7z) is subequal in length with the outer branch of the rhipidura, 

 and terminates in a long and lance-like point of extreme sharpness, on each side of which 

 are several small sharp spinules and one large one, from which the telson anteriorly 

 gradually widens to the base. The dorsal surface is deeply grooved and the sides 

 are compressed, the ridges so formed being armed with two distant rudimentary 

 spinules. 



Observations. — This species exhibits several features that are not common to those of 

 the genus Acanthephyra, and are suggestive of an approximation to Oplophorus, but the 

 resemblance is not complete. 



It has some resemblance to Acanthephyra purpurea, but may readily be distin- 

 guished by the character of the orbit, the largeness of the eyes, the lateral teeth on the 

 anterior margin of the first somite and on the posterior margins of the fourth and fifth 

 somites of the pleon, by the dorsal groove and the absence of a tooth in the median line 

 of the sixth somite, and by the form of the telson. 



It closely resembles Systellaspis (Acanthep>hyra) debilis, A. Milne-Edwards, from 

 which it may be determined by the number of the teeth on the dorsal crest of the 

 carapace and by the absence of a crenated margin at the posterior dorsal surface of the 

 fourth and fifth somites of the pleon. 



Oplophorus, Milne-Edwards. 



Oplophorus, Milne-Edwards, Hist. Nat. Crust., torn. ii. p. 423. 



Animal laterally compressed. Carapace about one-third the length of the body, 

 dorsally carinated, and supported on each side by a subcarina, and anteriorly pro- 

 duced to a long and slender rostrum that is serrate on the upper and lower margins. 

 Outer angle of the orbit defined by the first antennal tooth, which is curved inwards 

 between the ophthalmopoda and the second pair of antennae. The second antennal 

 tooth is directed forwards and the fronto-lateral angle is produced to a tooth that is 

 directed forwards and outwards, whence the lateral margin is abruptly directed inwards 

 and so continues until it unites again, at the posterior angle, with a strongly projecting 

 tooth. The posterior margin is but slightly produced laterally, and is compressed so as 

 to be overlapped by the first somite of the pleon, and has a tubercle that corresponds 



