BYTPIOCYTHERE. 209 



as to form an irregular reticulation ; lateral protuberance rounded and not very 

 prominent ; centre of the valves marked by a deep and vi^ide transverse sulcus. 

 Length, -^th of an inch. 



Distribution, Recent. — Great Britain, Ireland, Channel Islands. 



Fossil. — Scotland : Tangy Burn, Duntroon, Dumbarton, Govan. 



3. Bythocythere elongata, nov. sjj. Plate II, figs. 4, 5. 



Carapace, seen laterally, oblong, subelliptical, somewhat higher behind than in front, 

 height equal to less than one half of the length ; extremities rather obliquely rounded off; 

 superior margin almost straight for the greater part of its course, but sloping gently 

 towards the front ; inferior nearly straight. Seen from above, compressed, ovate, some- 

 what suddenly tapered and obtusely pointed in front, prominently mucronate behind ; 

 greatest width less than the height and situated rather behind the middle of the shell. 

 Shell transversely rugose in a waved manner, with a central transverse sulcus, such as is 

 frequently observed in this and the preceding genus. Lower surface of the shell marked 

 with longitudinal furrows. 



Length, -^qUi of an inch. 



This species, in general appearance, bears some resemblance to CytlLeropteron rectum, 

 especially in its rugose sculpture and rounded angles. 



Distribution. — One specimen only was found at Girvan. 



Genus 11 — Pseudocythere, G. 0. Sars. 



Shell thin and pellucid, having no distinct structure, rounded in front, produced 

 behind. Hinge-joint simple. Upper antennse bearing long setae, 7-jointed ; second joint 

 thick and armed with a single seta on the middle of the anterior margin ; last joint very 

 long and narrow, linear, terminating in very long setae ; lower antennae very slender, 

 5-jointed ; flagellum long and slender. Mandibles small, with slender, curved, unguiform, 

 teeth; palp narro-w, 4-jointed ; branchial appendage bearing long setae. Terminal lobes 

 of the first pair of jaws narrow ; branchial plate large, elongate-ovate, armed towards the 

 base with three curved and deflexed simple setae. Peet very long and slender. Abdo- 



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