MACRURA. SCHMITT. 321 



formula he gives for "Parapenceus" and this branchial 

 member is probably also to be found in P. rectacutus, 

 even though Alcock grouped that species with forms 

 lacking it. 



In addition to a re-examination of some of the 

 Metapenei examined by Alcock, and Penceopsis endeavour i 

 described below, a number of other species in the col- 

 lection of the United States National Museum have been 

 examined. These are acclivis (Rathbun), akayebi (Rath- 

 bun), dalei (Rathbun), incisipcs (Bate), intermedius 

 (Kishinouye), goodei (Smith), mobilispinis (Rathbun), 

 mogiensis (Rathbun), velutinus (Dana) (Rathbun), and 

 laniellatus (de Haan.). Only the latter appears to have 

 no trace of the vestigial arthrobranch so easily made out 

 on the penultimate pair of legs of all the other species, 

 and which, but for the inclusion of this species, I should 

 have regarded of great generic value. P. laniellatus has 

 a very hairy lobule on the posterior border of the articu- 

 lating membrane of each penultimate thoracic leg, but 

 it is neither in the position of, nor of the same character 

 as, the vestige found in the other species, and does not 

 represent an anterior arthrobranch. I find no other 

 characters to separate this species geuerically from its 

 fellows. 



In seeking other characters that might possibly 

 differentiate Penceopsis from Metapeneus, I noticed that 

 P. megalops and P. rectacutus had antennular flagella as 

 long as or longer than their peduncle, while all the other 

 "Metapenei" except "Metapeneus coniger" and its variety 

 "andamanensis" had quite short antenuular flagella, 

 noticeably shorter than their peduncles. These two 

 exceptions, of which the United States National Museum 

 fortunately possesses a male and female of the typical 

 species, and a male of the varietal form, have antennular 

 flagella which are about as long as their peduncle, and 

 what is more remarkable, the males have the inner 

 flagellum somewhat flattened proxirnally with "its inner 

 border concave ... up to a small conical denticle" 

 (Alcock, op. cit. p. 25), being thus constituted strikingly 

 like the corresponding flagella in P. megalops and P. 

 rectacutus. Moreover, the exopodites of "Metapencus 

 coniger" are quite small, tending to approach the scale- 

 like ones of P. megalops in their degree of reduction. 

 They are quite incorrectly figured by Alcock (op. cit.,, 



