D. J. SCOURFIELD ON EPHIPPIA OF LYNCEID ENTOMOSTRACA. 239 



The consequence of this is that a Lynceid ephippium usually 

 has a somewhat jagged ventral margin, due to the falling away or 

 otherwise of the little pieces of chitin referred to. In this respect 

 it differs from an ephippium of a Bosmiiui, in which the edges of 

 the crack always seem to be quite smooth. 



The object to be attained by the separation of the ventral 

 parts of the valves is, without doubt, the formation of a nearly 

 closed receptacle for the Qgg. It is evident that if the ventral 

 margins, and especially the strongly vaulted anterior j^ortions of 

 them, remained in position, the anterior edges of the valves could 

 not come together, and there would also usually be an opening 

 between the middle parts of the ventral margins, owing to the 

 noi-mal structure of the L3mceid shell. It is interesting to note 

 that in the only instance where the whole shell is used as an 

 ephippium (Alo7ia tenuicauclis) the egg is embedded in a great 

 mass of chitinons spongy tissue — although this is, to be sure, 

 not the only case in which the latter provision occurs. 



(5) The chitin of the valves of the ephippium is always more 

 or less darkened and probably thickened, but as a rule it is not 

 much modified, except that the ordinary shell sculj^ture becomes 

 at times intensified, and a minutely pitted structure is often 

 developed. 



In a great number of species it is quite easy to trace the 

 normal shell markings, both coarse and fine if present, over the 

 ephippium, and in no case do we find such a radical alteration of 

 the outer shell structure as is seen in the more highly evolved 

 ephippia of the Daphnidae, nor has any instance been observed 

 of an approach to the formation of an oblique lateral band of 

 chitin such as occurs in the Bosminidae. In some cases there 

 seems to be a decided tendency for the shell to swell out into a 

 more or less pronounced boss just over the Qgg, but this may be 

 due in part simply to the closing of the valves over the egg. 



(6) Between the outer valves of the ephippium and the egg 

 there are always certain membranes or Cellular tissue present, 

 forming probably in most cases a perfectly closed inner covering 

 for the egg. 



The nature of the inner membranes, etc., varies very much 

 indeed. In many, perhaps the majority of cases, the egg is 

 surrounded by extremely delicate membranes representing the 

 unmodified, or nearly unmodified, inner lining of the carapace. 



