380 Annals of the South African Museiim. 



but at the apices of two processes called penes peuial filaments or male- 

 stylets. Gerstaecker (I.e. p. 102) gives Idotea and Aega as examples in 

 which such processes are absent, and his figure of J. entomon supports 

 this. But this is certainly wrong for Idotea, unless I. entomon is an 

 exception, for in all the species of Idoteidae which I have examined 

 (all those recorded from South Africa and Plymouth) these processes 

 are very evident. As can be seen by dissection they are traversed by 

 the vasa deferentia. 



Thus it may be stated that in the Valvifera the vasa defereutia open 

 .at the end of styliform processes on the first pleon segment. 



But within the tribe the two main families are sharply divided by 

 the fact that the processes are separate in the Idoteidae * and united 

 into a single process in the Astaciilidae. At any rate this latter state- 

 ment is correct for all the South African species, for Astacilla longi- 

 cornis, Arcturella danmonensis, A. dilatata, Arcturus baffini, Antarcturus 

 antarcticus and A. meridionalis. I am indebted to Dr. Caiman for 

 examining the last four species. Thus I am unable to understand 

 Bate and Westwood's statement (I.e. p. 368) that in A. longicornis 

 " there is a pair of minute organs terminated by two somewhat 

 cultrate plates " ; in the specimens I have examined there is only a 

 single median process tapering slightly to a blunt apex. 



Similarly when Koehler (Bull. Inst. oc. Monaco, No. 214, p. 18), 

 describing the male of Arcturopsis senegalensis, says : " eutre les deux 

 pleopodes [de la premiere paire] se trouve le double penis habituel," 

 and again (I.e. p. 52) for Astacilla mediterranea, " le penis ... a 

 la forme habituelle," there must be some mistake in this author's 

 observation. Caiman also in 1909 (Lankester's Treatise Crust, 

 p. 212) states that there is only the single penis in the Arcturidae 

 ( = Astaciilidae') . 



The vasa defereutia still remain separate throughout their whole 

 length and open by separate orifices at the apex of the fused processes. 

 The coalescence of the two processes in the Astaciilidae is most probably 

 to be ascribed to the narrowing of the body. 



Unfortunately the published accounts of Amesopous richardsonae 

 Stebb. and Pseudidotea bonnieri Ohliu gave no indication of the 

 character of the copulatory processes in these intermediate families. 

 From the character of the first pleopod and the uropod in P. bonnieri 

 I feel sure that there is a single median process ; such is also probably 

 the case in A. richardsonae, but of this one cannot be certain. On 

 applying to Mr. Stebbing for light on this point, he very kindly re- 



* Synidotea hirtipes forms an exception, having a single process, which is, 

 however, not narrow as in the Astacillids but broad and apically blunt. 



