RECENT BRITISH OSTRACODA. 



427 



have already gained a certain currency, it seems best not to disturb the existing nomen- 

 clature for the sake of adherence to a law which, in this case, would further confuse 

 matters. 



5. Cytheridea lacustris (G. O. Sars). (Plate XXVI. figs. 18-21, and Plate XL. fig. 2.) 

 Cythere lacustris, G. O. Sars, Zoologisk Reise i Sommeren 1862, p. 30. 



CyjUrideis torosa, Jones (in part), Tertiary Entomostraca, p. 31, pi. ii. figs, \ a-\i, and woodcut, p. 16. fig. 2. 

 Distribution : Recent — Norway, Scotland. Fossil — Posttertiary, England. 



Valves of the female, as seen from the side oblong, subtriangular, highest in front ; 

 greatest height equal to more than half the length. Anterior margin broad and well 

 rounded; posterior narrowed, obscurely angular above, rounded off below. Superior 

 margin much elevated and angular over the anterior hinge, thence sloping steeply back- 

 wards in a right line ; inferior straight or very slightly sinuated in front of the middle. 

 Outline, as seen from above, oblong oval, irregularly emarginate ; sides nearly parallel ; 

 extremities equal and obtusely pointed ; width equal to half the length ; a deep longitu- 

 dinal sulcus formed by the depression of the hinge-margins behind the middle. The 

 ventral surface is marked with faint, jagged, longitudinal furrows. End view ovate, 

 broad below, pointed above. The shell is thick and dense in structure, covered with 

 closely set irregular pittings, and with scattered papillae, each of which seems to be com- 

 posed of four small points arranged in a rosulate manner ; often these are fused so as to 

 form one papilla with a central perforation. Valves transversely sulcate and bearing 

 several irregularly placed rounded tubercles. Colour pale yellowish brown. Hingement 

 that of Cytheridea, except that the terminal rounded protuberances are scarcely at all 

 crenated. Limbs very robust. Upper antennae short and stout ; terminal joint linear, 

 considerably longer than either of the two preceding joints, which are about equal in 

 length and very short ; the antepenultimate about equal to the following two ; spines 

 long and slender. Urticating seta of the lower antenna very short, reaching to the base 

 of the terminal claws. Basal joint of the first pair of feet very stout, about equal in 

 length to the three following joints, bearing on its posterior margin a very stout flexuous 

 seta ; second joint narrow at the base and much dilated at the distal extremity ; last 

 two joints very short, and distinctly separated ; terminal claw slender, slightly curved, 

 and equal in length to the three preceding joints. Second joint of the last pair much 

 longer than the following two, which, like those of the other feet, are much dilated at 

 the apex. Male unknown. 



Length in., height in. . <fo- < . S'^y^- 

 Hob. North Shaws Loch, Selkirkshire (G. B.); Glasgow and Paisley Canal [Mr. D. Robertson). 



I took one imperfect specimen of this very interesting species in Selkirkshire in 1864, 

 since which time Mr. E^obertson has found it more abundantly in the neighbourhood of 

 Glasgow. It occurs fossil in the fluviatile clays of Hornsea, Yorkshire ; and at Grays, in 

 Essex. 



3 M 2 



