PalcEOZoic Bivalved Entomostraca. 243 



This species much resembles some varieties of B. Kloedeni 

 (Annals Nat. Hist. 2 ser. vol. xvi. p. 166)^ in which the fore and 

 hind lobes are continuous, or nearly so, along the ventral part 

 of the valve. In B. clathrata, however, and in B. plagosa^y 

 there is no interruption of the ventral lobe at all, which has a 

 great relative breadth, like that in B. Wilckensiana, the type of 

 the " Corrugatse,^' or bisulcate group of Beyrichice (Annals Nat. 

 Hist. 2 ser. vol. xvi. p. 85). 



In B. Kloedeni, as in B. tuherculata, the ornamentation takes 

 a granulate form ; in the Beyrichics from Beechey Island, on the 

 contrary, it is in intaglio. 



4. Beyrichia plagosttj spec. nov. PI. IX. fig. 2. 



Length -^q, breadth ^-^ inch. 



This belongs also to the bisulcate type, and has a large semi- 

 circular, and a small, oval, subcentral lobe; but the former is 

 traversed along its length by several more or less parallel and 

 concentric, but irregular, sunken lines, dividing the lobe into 

 about four large and six small convex stripes, of unequal pro- 

 portions. 



The whole surface is impressed by a system of minute chan- 

 nels, coarsely reticulate. 



From Beechey Island, with the foregoing. 



The Beyrichice from Beechey Island occur in considerable 

 numbers, in company with Leperditia gibbera (Annals Nat. Hist. 

 2 ser. vol. xvii. p. 90), in a small piece of dark-coloured limestone 

 brought to England by Capt. Sir E. Belcher. Like the L, gib- 

 bera, all the Beyrichia in this rock retain their shells, which 

 exhibit a glossy surface and a brown colour. 



For a Cytheropsis from Beechey Island, see p. 254. 



* These two species were referred to, as being probably two varieties of 

 jB. Kloedeni, in Annals Nat. Hist. 2 ser. vol. vi. p. 91, but a careful examina- 

 tion has led me to regard them as certainly distinct from that species. 

 With respect to their difference one from another, — although they have 

 much in common as to their outline and general form, — though the 

 ornament of B. clathrata may be the rudimentary state of the reticulation 

 of B. plagosa, and though the plaiting of the latter is, as it were, begun in 

 the anterior lobe of B. clathrata, yet, in accordance with the plan which 

 we must adopt with fossil remains in which evidences of the soft parts 

 are wanting, and which we are desirous of rendering useful palaeonto- 

 logical witnesses of former races, I have given full weight to the differ- 

 ences of structure, and regarded these two Beyrichics as species and not 

 varieties. 



ir3* 



