REPORT ON THE CRUSTACEA MACRURA. 



11J 



Fig. 26. — Third pair of pleopoda 

 of Pentacheles euthrix 9 . 

 From a drawing by Willemoes- 

 Suhm. 



Fig. 27.— Terminal portion 

 of the Stylamblys. 



The four succeeding pairs of pleopoda are biramose and resemble each other, differing 

 in the male and female in having the first pair furnished with two stylamblydes on the 

 inner margin of the inner branch in the male, and with one in the female, as in all the 

 other pairs. Under a low magnifying power of the microscope the extremity of a 

 stylamblys in either sex, with but few exceptions, is furnished with small, blunt, hook-like 

 points, which Sars has named cincinnuli. 

 They are mostly rudimentary in this group 

 of animals ; but in others, as we shall show in 

 the Penaeidee, they efficiently fulfil an im- 

 portant office. 



The sixth pair of pleopoda is broad, large, 

 and powerful, and goes to form the outer 

 plates of the rhipidura or tail-fan, which in 

 these animals is a powerful and much used 

 appendage, of which the telson forms the 

 central part. 



The relation that this animal bears to 

 other forms of recent Crustacea shows that, in its structure and in the depressed character, 

 it lies near the genus Arctus of the Scyllaridse, the chief distinctions being in the form of 

 the second pair of antennae, and in the direction of the antero-lateral angle of the 

 carapace, which is thrown forwards instead of outwards. After this all resemblance 

 appears to cease ; for, with the exception of a modified resemblance of the first and 

 second pairs of the oral appendages (siagnopoda), every appendage essentially differs. 



There is an animal which has been alluded to in the present Report (p. 88) under the 

 name of Synaxps hybrklica, 1 that has much the character of a genus of the Scyllaridse, 

 but it possesses a long flagellum attached to the second pair of antennae, which are large 

 powerful organs without any scaphocerite, and are situated beneath the eyes, as in Poly- 

 cheles ; but the first pair, instead of being pressed close together as in that species, 

 are forced down to a line horizontally lower than the second pair. The eyes are small 

 but efficiently developed, and are situated in an orbit less perfectly formed than that of 

 any of the Scyllaridse, and more like that which exists in Polycheles, &c. ; and is formed, 

 as in that genus, by the anterior projection of the antennal angle of the carapace. All 

 the other features of the animal- — the pereiopoda, pleopoda, rhipidura, &c. — resemble those 

 of Arctus, except that in the female the fifth pair of pereiopoda is simple in form, 

 whereas in Arctus, and in the Scyllaridse generally, it is chelate. 



A near and interesting connection with Synaxes is to be found in the fossil described 

 by Miinster, 2 and reproduced by Woodward in his Chart of Fossil Crustacea, under the 

 name of Cancrinus clavigei, from the Upper White Jurassic Limestone of Bavaria. 



1 Ann. and Mag. Nat. Hist., ser. 5, vol. vii. p. 221, pi. xiv. 



2 MiiDster, pt. ii. t. 15, fig. 1. 



