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



fringed with hairs ; the outer branch is always the larger and more conspicuous in the 

 anterior pairs, the inner gradually lessening in proportion as it advances until it is little 

 more than rudimentary in the first pair. 



The sixth pair of pleopoda forms the outer plates of the rhipidura : the basal joint is 

 short, the outer plate is longer than the inner, and the inner is longer than the telson, 

 and both graduate towards the outer distal angle of the external branch. 



Observations. — Both our specimens, which were purchased in the market at Yokohama, 

 are females, and have the very peculiar apparatus on the ventral surface between the 

 posterior pair of pereiopoda, which, so far as I am aware, has never been previously 

 figured or described by any naturalist. 



The female of a variety taken at Port Jackson agrees with the Japanese form in every 

 detail excepting that the thelycum consists of two oval plates attached in their entire 

 width, at the posterior extremity to the ventral surface of the pereion, and at the anterior 

 by a narrow process on the outer side only. This organ differs in form from the 

 thelycum in the Japanese variety. I have only examined females of this species, and 

 my experience of this peculiar apparatus is not sufficiently extensive to enable me to say 

 whether or not it undergoes any change or modification of form or of growth on the 

 approach of the power of reproduction. 



Penseuscanaliculatus, var. australiensis, nov. (PL XXXII. fig. 3). 



This variety corresponds closely with the preceding, but differs in the form of the 

 thelycum, which may be better understood by the figure on the plate than by a written 

 description. There are, moreover, plates on the ventral surface, between the third and 

 fourth pairs of pereiopoda, that are not apparent in the typical varieties. 



There is not a male of this variety in the collection. 



Length (female), 100 mm. (4 in.). 



Habitat. — Port Jackson, Australia; depth 2 to 10 fathoms; April 1874. 



Penseus indicus, Milne-Edwards (PI. XXXIII. fig. 2). 



Penxus indicus, Milne-Edwards, Hist. Nat. Crust., tom. ii. p. 415. 



„ „ Sp. B., Ann. and Mag. Nat. Hist., ser. 5, vol. viii. p. 177, pi. xii. fig. 5. 



Rostrum straight, just passing beyond the extremity of the peduncle of the first pair 

 of antennae, styliform towards the extremity, and surmounted at the base by a crest 

 that gradually decreases towards the posterior margin of the carapace. Armed with 

 eight (" or nine ") teeth on the dorsal surface, and four or five on the inferior. Flagella 

 of the first pair of antennas slender and equal in length to their peduncle. Telson about 

 half the length of the outer branch of the rhipidura, terminating in a sharp point, with 





