REPORT ON THE CRUSTACEA MACRURA. 



109 



Fig. 24.— The lower ami 

 larger branchial plume of 

 the first pair of pereiopoda, 

 with tlagelliform appen- 

 dage of Pentacheles eu- 

 thrix. From note and draw- 

 ing by Willemoes-Suhni. 



mastis suhmi it is altogether wanting, ami the podobranchia is reduced to an iilmost 

 rudimentary condition. 



The second pair of pereiopoda is much shorter, and assumes more the form usual in a 

 chelate appendage, the fingers being slender and apparently more 

 perfectly adapted for secure prehension. It is probably with this 

 pair of appendages that the animal usually feeds itself. 



The two succeeding pairs (PI. XX. m) are also always chelate, 

 but the fingers are long and tapering, and are generally both curved 

 in the same parallel direction posteriorly, a circumstance that gives 

 them a very feeble appearance. 



The fifth pair is shorter than the rest, and varies from the simple 

 styliform condition to that of a small and perfect chela, varying some- 

 times with the sex and sometimes existing as a specific character. 



In Polycheles the male has this pair of appendages simple, but in 

 the female it has not been determined in any species except Poly- 

 cheles baccata, where it is chelate, but stunted and imperfect in form. 

 The female of Polycheles crucifera is not known ; while that of 

 Polychdes helleri is unfortunately injured, so that the termination of 

 the appendage cannot be made out. Professor Camil Heller says that he only knew of 

 a male specimen of Polycheles typhlops, and the specimens . taken during the cruise of 

 the "Porcupine " have not yet been determined in their specific relation to each other. 1 



In the genus Pentacheles the posterior pair of pereiopoda is chelate in both sexes, and 

 in most species the fingers are of unequal length. They are more nearly equal in 

 Pentacheles euthrix than in any other; but in those species in which both sexes have 

 been determined, as Stereomastis auriculata and Stereomastis suhmi, the female has the 

 fingers as unequally developed, or nearly so, as the male ; and it is because of this feature 

 that I have arranged the species gracilis and obscura under the genus Pentacheles rather 

 than under Polycheles. 



The branchial arrangement (PI. XX. fig. 1) is based on the same type throughout, 

 and consists of sixteen branchial plumes on each side, with or without mastigobranchial 

 plates of more or less importance, being large in Willemcesia and wanting in Stereomastis 

 suhmi and Stereomastis auriculata in all the pereiopoda, and reduced to a small or 

 rudimentary condition on the second gnathopoda, and absent from the first in all excepting 

 Pentacheles euthrix, where it is only imperfectly represented ; while it is developed into 

 large plates on the two posterior siagnopoda. 



The podobranchia! plumes are generally large and well developed, except in the first 



1 In his Remarks on the Recent Eryontidre, the Rev. Dr. Norman (Ann. and Mag. Nat. Hist., ser. 5, vol. iv. 

 p. 176, 1879) states that of the two specimens taken by H.M.S. "Porcupine" the female differs from the male in having 

 " on front margin a pair of central spines (instead of a single spine)," besides indicating other differences that appear 

 to be more than sexual characters. 



