SCHEROCHILUS. 211 



Cytherideis subspiralis, 710V. sp. Plate X, figs. 16, 17. 



Valves, as seen from the side, oblong, depressed in front, height equal to not much 

 more than one third of the length ; extremities rounded ; the anterior much narrowed ; 

 superior margin straight, but suddenly sloping forwards with a gentle declivity from 

 about the anterior third ; inferior margin almost straight. Seen from above, com- 

 pressed, ovate. Shell-surface marked with several curved or transversely spiral furrows, 

 and on the anterior half with distant circular pittings. 

 Length, -^th of an inch. 



Except the British C. suhulata, the only near relative of this curious species, with 

 which we are acquainted, is a still more compressed and elongated form found living in 

 the Mediterranean and amongst the Cape de Verd Islands, and described by Mr. Brady, 

 in ' Les Fonds de la Mer,' under the name Cytherideis cylindrica. One valve only of 

 C. subspiralis has been discovered. 



Distribution. Fossil. — Scotland : Wick. 



Genus 1 3 — Sclerochilus, G. 0. Sars. 



Valves elongated, very hard, especially towards the margins ; surface smooth and 

 shining, ornamented with very minute scattered papillae. Hinge-joint formed by a pro- 

 jecting median crest of the left valve. Lucid spots linear, subparallel, forming an oblique 

 oval patch below the centre of the valve. Antennae robust ; second joint of the upper 

 bearing a seta on the anterior and posterior margins, the last five joints quickly 

 decreasing in size and bearing numerous long setae ; lower antennae larger than the 

 upper, 5 -jointed ; flagellum long and very slender. Poison-glands very large, and 

 divided into many lobes. Mouth produced, conical ; labrum strongly toothed. Man- 

 dibles small ; teeth numerous and acuminate ; palp narrow, indistinctly 3-jointed, with 

 a distinct branchial appendage. Terminal lobes of the first pair of jaws partly wanting ; 

 branchial plate narrow, almost lanceolate, and beset with numerous setae on the outer 

 and inner margins. Feet short and robust ; second and third joints armed in front 

 with a sharp seta; first pair armed with a single strong spine at the apex of the 

 basal joint. Post-abdominal lobes larger than usual, forming broad bilobed laminae, and 

 bearing five setae. Eye single. 



