450 



MR. G. S. BRADY'S MONOGRAPH OF 



angular fossae, arranged in more or less distinct longitudinal rows, which are separated by- 

 sharp ridges. Colour yellowish brown. Animal unknown. 

 Length -^in. - 



Hab. In depths of 10-60 fathoms, Shetland, Stornoway, Skye, Loch Fyne, Plymouth [Rev. A. M. Norman) ; 

 Oban and Ormeshead {Mr. D. Robertson) ; Aberdeenshire [Mr. Dawson) ; Northumberland and 

 Durham coasts, 25-46 fathoms (G. S. B.) ; Hebrides, the Minch, and Channel Islands {Mr. J. G. 

 Jeffreys) ; Devonshire coast {Mr. C. Spence Bate) ; Roundstone {Dr. Alcock) . 



6. Cytheropteron rectum, nov. sp. {See Appendix.) 



Genus 10. Bythocythere, G. O. Sars. 



Valves subequal, smooth or very sparingly sculptured, almost destitute of hairs ; thin 

 and fragile. Hinge-joint quite simple or composed of a slight bar and furrow ; no teeth. 

 Upper antennae elongated, seven-jointed ; the second joint large and thick and bearing a 

 seta on its anterior and posterior margins ; the other joints suddenly much narrower, 

 forming a long slender lash, which bears several setse; penultimate joint linear and 

 destitute of setse. Lower antennae tolerably robust, four-jointed; second joint large; 

 flagellum long, biarticulate, its last joint long and setiform. Mandibles constricted above 

 the distal extremity, strongly toothed ; palp four-jointed, bearing a well-developed bran- 

 chial plate, which is set with numerous ciliated setse. Terminal lobes of the first pair of 

 jaws very short and thick ; branchial plate large, ovate, bearing numerous marginal 

 ciliated setse, and at the base four long and deflexed simple setse. Peet elongated, 

 terminal claw very long and slender, second and third joints bearing each a short apical 

 seta ; basal joint of the first pair furnished at the base with a small lobe, which bears two 

 very large and densely ciliated, and two smaller and simple setse. Abdomen ending in a 

 very large and acuminated process ; postabdominal lobes narrow and bearing three hairs. 

 Eyes mostly absent. 



The species grouped under this genus present two very distinct types, so far as the 

 characters of the shell are concerned ; but according to the investigations of Herr G. O. 

 Sars, the structure of the animal itself is the same in both types. My own observations 

 of the animal have been made altogether on dried specimens, and are necessarily 

 imperfect, but, so far as they go, they are quite in accordance with those of that most 

 accurate author. 



1. Bythocythere simplex (Norman). (Plate XXXIII. figs. 23-27, and Plate XL. fig. 8.) 



Cythere simplex, Norman, Nat. Hist. Trans. Northumb. & Durh. vol. i. p. 17, pi. v. figs. 1-4. 

 Jonesia simplex, Brady, Trans. Zool. Soc. Lond. vol. v. p. 363, pi. Ivii. figs, lla-e. 

 Bythocythere acuminata, G. O. Sars, loc. cit. p. 86. 



Scandinavian type. Distribution : Recent — Baffin^s Bay, Norway, Britain. Fossil — Glacial, Scotland. 



Carapace of the female, as seen from the side, oblong fusiform, about twice and a half 

 as long as broad, rounded in front, acuminate behind. Dorsal margin straight in the 

 middle, sloping suddenly downwards at the posterior extremity, gently rounded in front ; 



