some British Fossil Crustacea. 395 



a point, the inner edge being straight and simple, the outer edge 

 slightly convex. The hands of both kinds of chelse are similarly 

 sculptured with short, fine, sharp, irregularly curved, longitu- 

 dinal plicae, proving their identity, and that thus, like the recent 

 Poecilopoda, more than one pair of feet were didactyle. 



In the fine olive schists (of the age of the Upper Ludlow 

 rock) of Leintwardine. 



(Col. University of Cambridge.) 



Trib. Phyllopoda {= Branchiopoda, M. Edw.). 



This tribe might be divided into the five following families, 

 all having membranous feet : — 



1. Daphniad^iE (= Cladocera). Carapace oval, compressed, the 

 posterior portion bivalve, inclosing the body, the anterior end 

 forming a separate beak-shaped hood for the head. Eye sin- 

 gle, semicompound*. Feet, only four pair, foliaceous. An- 

 tenna, first pair small ; second pair very large, branched and 

 bristled for swimming. (Type Daphnia, &c.) 



The Daphnia ? primceva (M'Coy), Syn. Carb. Foss. Irel. t. 23. 

 f. 5, is the only probable example of this family I know in the 

 fossil state. 



2. BRANCHiPODiADyE. Carapace none, all the body-rings di- 

 stinct and naked. (Type Branchipus.) 



I know of no fossil example of this group. 



3. TRiLOBiTADiE (= Palcsadce). Head and abdomen covered by 

 separate dorsal shields, thoracic segments naked, separately 

 moveable, generally trilobed by two longitudinal depressions. 

 Eyes two, large, semicompound, or absent. 



This very extensive group is only known in the fossil state, 

 and apparently confined to the palaeozoic rocks. I will ofi'er some 

 observations of detail below. 



4. Apodiad^. Carapace a semi-oval, horizontal shield, not 

 covering the abdominal segments, which are distinct. Eyes, 

 one simple and two large semicompound ones. Feet, about 

 60 pair. (Type Apus.) 



The carboniferous genus Dithyr^ocaris is I think referrible to 

 this group, though I have not yet detected the eyes. (See Syn. 

 Carb. Foss. Irel. t. 23. f. 2.) 



* I use this term to particularize that type of eye so common among the 

 Entomostvaca, in which a 7nass of ni'mute eyes are covered by one simple, 

 uiidiolded, External cornea, being thus intermediate between the simple eye, 

 and the true compound eye in which the external cornea is faceted, and 

 divided into as many portions as there are eyes beneath. 



