278 Major A. Alcock and Capt. A. R. S. Anderson on 



XLIII. — Natural History Notes from H.M. Boyal Indian 

 Marine Survey S/iip * Investigator ^^ Commander T. II. 

 Ueming, B.N., commanding. — Series III., No. 2. An 

 Account of the Deep-sea Crustacea dredged during the Sur- 

 veying-season of 1S97-98. By A. Alcock, ]\Iaior, Indian 

 Medical Service, Superintendent of the Indian Museum, and 

 A. R. S. Anderson, Captain, Indian Medical Service, 

 Surgeon-Naturalist to the Survey. 



[Continued from p. 27.] 



MACRURA. 



Family Penaeidae. 



Pen^us, Fabr. 



Penceus rectacutus, Sp. Bate. 



Penceus rectacutus, Sp. Bate, * Challenger ' Macrura, p. 2G6, pi. xxvi 



lig. 2 (exc. 2 z). 

 Metapenaus rectaciitns, Wood-Mason & Alcock, Ann. & Mag. Nat. 



Hist., Oct. ]891, pp. 274, 275. 



Spence Bate suggests that Penoius serratus and Penceus 

 rectacutus may prove to be the same species. The former, of 

 which there are two * Challenger ' specimens from Fiji in the 

 Indian Museum, possesses no epipodite on the twelfth seg- 

 ment, while the latter has one. 



In the males of this species the outer branch of the an- 

 tennulary flagellum is about twice the length of the inner 

 and has a very stout base suddenly narrowing and tapering 

 into a long filamentous extremity; from about the middle of 

 the lower and inner side of this thickened base a small sharp 

 conical tooth, as in Metapenceus coniger^ projects ; the inner 

 braiich is horizontally flattened in the proximal quarter of its 

 length, and here forms a rigid semicircular loop downwards 

 below the outer branch, as in Penceus serratus; on again 

 reaching the level of the outer branch it gives off a small 

 flattened hooked process articulating with the conical tooth on 

 the outer branch, and becoming twisted on itself, and so 

 vertically flattened lies alongside and in close apposition to 

 the outer branch. Towards its extremity the inner branch 

 becomes thin and filiform like the outer. 



The absence of a rudimentary anterior arthrobranchia from 

 the thirteenth segment seems to exclude this species from 

 "Wood-Mason's genus Metapenasus. 



4 (^,3 ? , from Station 235, 370-419 fathoms. 



