572 Mil. AV. r. LANCIIESTEJI ON TUB [Dec. 3, 



are quite as long as the peduncles. In these respects it more 

 resembles the P. lysianassa de Man (Mergui Crust, p. 291), but 

 in that species the rostrum is even shorter, nor do the antenuulary 

 peduncles reach the ends of the autenual scales ; moreover, the 

 petasma, though somewhat similar, is still distinctly different. 



87, Penults affinis Sp. Bate. 



Penciius affinis, Sp. Bate, Ann. Mag. Nat. Hist. (5) viii. p. 179, 

 pi. xii. fig. 6 (1881). 



Loc. Pulau Bidan, Penang. 



A female ; length 38 mm. 



The apex, i. e. anterior edge, of the heart-shaped theljcum in 

 this specimen is, as it Avere, frayed out into very minute teeth, 

 only visible under a lens. 



88. PEXyTiUS MUTATus, sp. u. (Plate XXXIV. fig. 6.) 



Cf. Penoius monoceros (Fabr.), de Man, Weber's Zool. Ergebu. 

 p. 513, pi. xxix. fig. 54 (1892) ; and P. lysianassa, id. Mergui 

 Crust, p. 290, pi. xix. fig. 1 (1888). 



Loc. — — ? A male and a female. 



This species, although showing close affinities with Peiutus 

 monoceros by its general structure, yet presents in the male certain 

 modifications (in the form of the petasma, 5th pair of legs, and 

 telson) that closely resemble similar modifications in P. lysianassa ; 

 while the thelycum in the female, though very like that in P. mono- 

 ceros, yet again shows a modification in structure which, so far as 

 1 know, has hitherto been described in only one other species. 



In regard to its general structure it agrees, as I have said, 

 closely with P. m.onoceros, and the description given by Dr. de Man 

 {t. c. supra) for a female of that species applies equally well to 

 these two individuals ; with the exception that the legs are shorter, 

 so that the 1st pair reach barely to the ends of the eye-stalks (i. e. 

 the eyes not included), the 2nd pair reach only to the middle of 

 the scaphocerites,the 3rd only to the tip of the spine at the outer 

 distal angle of the scaphocerites, the 4th ai*e as long as the 1st ; 

 the 5th, however, are longer than the 2nd by their last joint. 



The petasma is remarkably like that in P. lysianassa, and so 

 peculiar that I refer to the figure for its structure ; it appears to 

 differ cliiefly in the structure of its anterior surface, which, instead 

 of bearing t wo pairs of dentiform prominences, one at its base and 

 one at its distal extremity, bears one pair at the base directed 

 towards the ventral surface of the abdomen, and just above this 

 pair another pair of low, bluntly triangular, prominences directed 

 inwardly towards each other (vide fig. 6 b). 



The thelycum is shaped much as in P. monoceros {cf. de Man, 

 he. fig. 54 rt; Ortmann, Zool. Jahrb. v. pi. xxxAd. fig. 36), 

 with some slight diff'erences best brought out by the figure. 

 But, in addition to this, there are also a pair of small plate-like 

 structures which abut against the outer sides of that grooved 

 part of the thelycum which extends forwards towards the 



