CYPHODEE1A TROCHUS. 83 



The test in this variety is similar in form to that of 

 C. ampulla, but is composed of the imbricated discs 

 which are typical of G. trochus. The discs usually vary 

 from 4 to 5 /x in diameter, but sometimes do not exceed 

 3'5/A, becoming even smaller, 3*5 to 2*75 /A, towards 

 the apex ; the amount of imbrication is also variable, as 

 shown in figs. 149 and 150 ; the markings where three 

 or four scales overlap, although similar in disposition 

 are quite different in origin and appearance from the 

 perforations in the tests of C. ampulla var. major. 



The exposed edges of the scales occasionally have 

 a dentate appearance which is probably due to the 

 disposition of the chitinous cement by which they are 

 fastened together. 



In the few districts which we have investigated 

 fairly thoroughly, i. e. North Riding of Yorkshire and 

 Western Mayo, this variety is not uncommon, and it 

 will no doubt be found to be widely distributed in the 

 British Isles. Either this variety or var. palustris is 

 probably the prototype of G. trochus sensu stricta, an 

 exclusively deep-water form. $ome of the records of 

 G. ampulla doubtless refer to it. 



Genus 38. CAMPASCUS Leidy, J877. 

 LEIDY in Proc. Acad. Philad. 1877, p. 294. 



Test retort-shaped with curved neck, composed of 

 a chitinous pellicle with a covering of amorphous 

 scales; transverse section trigonal with rounded 

 angles ; aperture circular, oblique, furnished with a 

 thin, transparent, disc-shaped collar ; nucleus large 

 with several nucleoles, placed posteriorly ; one or more 

 contractile vesicles; plasma similar to that of the 

 Gyphoderide ; pseudopodia few, straight, filose, un- 

 branched. 



In the form of the test, and in the constitution of 

 and inclusions in the plasma, the members of this 

 genus are very closely allied to the Gyphoderide; they 



