D. J. SCOURFIELD ON EPHIPPIA OF LYXCEID ENTOMOSTRACA. 241 



and thickening of the valves dorsally, while, more important still, 

 there is a highly evolved " packing " produced as a further 

 protection for the egg. And in the least specialised of the 

 remaining ephippia there is always, in addition to a certain 

 amount of darkening and thickening, a special line of weakness 

 formed with the object of allowing the anterior ventral portions 

 of the valves to be detached. In the more highly specialised 

 forms we find a rather greater amount of thickening and 

 ■darkening, a larger portion, or the whole, of the ventral margin 

 detached, and some increase or other modification of the inner 

 membrane ; whilst in the most highly specialised form of all, 

 Leydigia acanthucercoides^ the same modifications become still 

 more marked, with the additional feature of hooklike appendages, 

 so that we get an ephijDpium which, in certain respects, is more 

 elaborately formed than many of those of the Daphnidae. As, 

 however, none of these Lynceid ephippia possess any trace of the 

 pecuHar prismatic cell structure of the outer coat foTind in the 

 ephippia of all the Daphnidae and some Lyncodaphnidae, we 

 can still regard them as forming, together with those of the 

 Bosminidae, a distinct, and, on the whole, a lower type, to which 

 the term " proto-ephippium " may be applied, as proposed in the 

 article on Chydorus sj^haericus (9). The use of a special word is, 

 perhaps, hardly necessary in ordinary circumstances, and I have 

 preferred to use the well-known word ''ephippium" throughout 

 this paper. 



It might be thought strange if, in a paper dealing with ephippia, 

 no mention were made as to the most likely times to find such 

 objects ; so I will devote a few words to this subject, trusting that 

 it may induce collectors of pond-life to be on the look-out for these 

 peculiar productions. In this country — and the same is probably 

 approximately true for the whole of the north temperate zone — 

 ephippia are produced most abundantly, and by the greatest 

 number of species, in the autumn and early winter (latter end of 

 September to the early part of December), the maximum pro- 

 duction being reached in October and November. In addition to 

 this main period of development there is always another in late 

 spring, with its maximum in May, which only seems to affect the 

 individuals Living in pools and little ponds liable to dry up in the 

 summer. It may sometimes happen that ephippia are formed 

 at other seasons of the year. I have myself seen an ephippial 



