25S Dr. W. T. Cnlman on fhp. 



XXIV. — On the Cnistacean Genus Sicvonellaj Borradu'ik. 

 By W. T. Calm AX, D.'Sc. 



(rublislied by penuissioii of the Trustees of the British Museum.) 



Sexce the publication of my recent paper on AphareocarU, 

 Dr. II. Balss of Munich has kindly drawn my attention 

 to the similarity between this genus and Sicyonella, estab- 

 lished by Borradaile in 1910 for a species obtained by 

 Prof. J. Stanley Gardiner in the Western Indian Ocean, By 

 the kindness of Mr. Borradaile and of Mr. L. Doncaster, 

 Supeiintendcnt of the Museum of Zoolojiy, Cambridge, I 

 liave been able to examine the type-material of Sicyonella 

 inaldivensis, with the result that this species proves to be 

 identical with my Aphareocaris eletjam from Torres Straits. 

 The synonymy of the genus must therefore stand as 

 follows : — 



Genus Sicyonella, Bori'adaile. 



Aphnreiis, Paulson, Izslyedovaniya Kakoobraznuikh Krasnagho Morya, 



Kiev, 187.5, p. 117. (Xoni. praeocc.) 

 Sia/oiiella, Borradaile, Trans. Linn. Soc, Zool. xiii. 1910, p. 2o9. 

 Aphareocaris, Caiman, Journ. Limi, Soc, Zuol. xxxii. 1913, p. 210. 



The discrepancies between Borradaile's description and 

 mine are, for the most part, easily explained on comparing 

 the type-specimens. The " antennal teeth ^' of the carapace 

 in Horradaile's account are really supraorbital in position, 

 while his " branchiostegal " tooth is that which I called 

 hepatic. The relative length of the third maxillipeds and 

 the subdivision of their terminal segments are exactly 

 similar in the two ibrms. In dealing with tlie branchial 

 system Borradaile has (1) reckoned as arthrobranchs the 

 ])i)dol)ranch of the second niaxilliped and t\\() anterior plcuro- 

 branchs of the five following somites, (2) assigned to the last 

 thoracic soniitc the posterior pleurobranch of the somite in 

 front, and (3) omitted to notice the vestigial pleurobranchs. 

 On all these points error is very easy, and even carel'ul 

 examination may leave room for (liffcrence of o|)inion, hut 

 I still i)elicvc that my version of the branchial formula is 

 snbstantially correct. 



The most serious obstacle to th:; identification of the two 

 species is that presented by the j)ctasma. As IJorradailo's 

 fignreof this is on a small scale I giv(; an (Milargcd figure 

 taken from one of his specimens, from which it will be seen 

 that the organ dillcrs widely from that figured in my forinor 

 paper, especially in the complex bianchiiig ol' the middlo 



