DARWINELLA. 



141 



and divided into several slender, curved spines ; bearing a large, three-jointed, pediform 

 palp, and an ovate branchial appendage of moderate size. Two pairs of feet of moderate 

 length, five-jointed, the second pair being much the longest, and having the last joint 

 armed with one long and two small curved setaj ; first three joints of nearly equal length, 

 fourth and fifth respectively about one half and one third as long as the preceding. 

 Abdomen ending in a short conical process. Copulative organs of the male of complex 

 structure, the basal portion, on each side, consisting of a subrhomboidal acuminate 

 lamina, the apical portion of an irregularly shaped plate produced laterally into an 

 alseform process, and on the distal margin into a short, strong hook. Female probably 

 viviparous. 



Darwinella Stbvensoni, Bradi/ and Bohertso?i. Plate II, figs. IB — 17. 



18/0. PoLYCHELES Stevensoni, B. & R. Anil. N. H., 1870, vol. vi., p. 25, plate vii, 



figs. 1 — 7, and pi. x, figs. 4 — 14. 

 1872. Dakwinella — B. & R. lb., vol. ix, p. 50. 



Carapace of the female as seen from the side, oblong, depressed in front, height equal 

 to more than one third of the length ; extremities obliquely rounded, anterior narrowed, 

 posterior broad and obtuse ; superior margin nearly straight, curving downwards in front 

 of the middle ; inferior shghtly sinuated in the middle. Seen from above, ovate, acu- 

 minate, widest near the posterior extremity ; greatest width about equal to the height ; 

 posterior margin indented in the middle at the junction of the two valves ; end view 

 nearly circular. Shell of the male somewhat more compressed when seen from above and 

 having the greatest width near the middle. The right valve much overlaps the left, 

 especially in the middle of the ventral margin. 

 Length, -^a-nd of an inch. 



Distribution. Recent. — England, Ireland, and Holland. 



Fossil. — England : Whittlesea. 



Famili/ 3.— CYTHERIDyE. 



Genus 1. — Cythere, Miiller. 



Valves unequal, mostly oblong-ovate, subreniform or subquadrangular ; surface 

 variously ornamented, — smooth, punctate, foveolate, strongly rugose, spinous, or tuber- 



