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



Cheramus, n. gen. 



This genus resembles Callianassa generally, but differs in having the second pair of 

 gnathopoda pediform ; in the form of the second pair of pleopoda ; in the third and 

 following pairs being ciliated, and in having strong spines, more or less curved, on the 

 posterior margin of the rhipidura. 



Observations. — In Callianassa, according to Milne-Edwards's figure and description, 1 

 the second pair of gnathopoda is broad and operculiform, whereas Leach 2 describes and 

 figures the same as being pediform. Bell 3 says that the same part is very broad, 

 but does not give a figure of the structure, although the specimen that he is describing- 

 belongs to Callianassa subterranea, the same species from which Leach and Edwards 

 drew their descriptions. 



De Haan 4 describes the part as being dilated, but figures it as being pediform; 

 whereas Dana, in his description of the genus, has overlooked it altogether. 



I have thought it desirable, therefore, to separate those in which the second pair of 

 gnathopoda are pediform from those in which they are operculiform, although feeling it 

 not improbable that further investigation may show that the two forms may be dependent 

 on either difference of age or sexual distinction, although such a condition is not usual. 



Cheramus orientalis, n. sp. (PL I. fig. 2). 



Carapace smooth, with a short pointed rostrum. Branchial regions distinctly 

 defined from the gastric and cardiac. Second pair of gnathopoda pediform. 

 Posterior pair of pleopoda having the outer plate much larger than the inner. Telson 

 long, cpiadrate. 



Habitat— Station 188, September 10, 1874; lat. 9° 59' S., long. 139° 42' E.; 

 Arafura Sea ; depth, 28 fathoms ; bottom, green mud. 



Length, 12 - 5 mm. (half an inch). 



There was but a single specimen taken, and this, unfortunately, in a very 

 damaged condition ; all the limbs were broken off except the first pair of antennae, the 

 oral appendages, one of the posterior pair of pereiopoda, and some of the pleopoda. 



It resembles Callianassa in its general appearance ; but the second pair of gnatho- 

 poda does not form an efficient operculum. 



The ophthalmopoda are horizontally compressed, and formed like a disk with a 

 pointed extremity, the eye being situated in the middle of the outer surface. 



1 " Les pates machoires externes sont operculiformes," Hist. Nat. des Crust., vol. ii. p. 308, pi. xxv. bis, fig. 2. 



2 " Palpi pediformes articulo secundo corupresso longiore," Malac. Pod. Brit., pi. xxxii. 



3 " External pedipalps, with the second and third joints very broad, constituting when in contact a broad oval 

 disk and terminating in a small seta formed of the last three joints," Hist. Brit. Stalk-Eyed Crustacea, p. 217. 



4 " Max illarum palpi nulli, art. 2 1 et 3 U dilatati," Siebold's Fauna Japonica, Crustacea, p. 162 tab. v. 



