Boring MoUusca of St. Andrexcs:. 373 



only a minute quantity of fine debris lodged under the ridges 

 wliicli gives the lilac coloration. 



The sensory powers of Zirphcea are worthy of note. 



The animal is sensitive to vibration, but does not appear 

 to be aware of sounds otlier than tiiose that sliake the water 

 in the tank. Tapping, singing, and shouting are noticed; 

 they are, however, not noticed immediately, but after a short 

 interval, sufficient to allow the disturbance to travel through 

 the water. The power of noticing vibrations is probably 

 helpful to the animal in boring, as a means of distinguishing 

 the direction in which lies solid and unshaken rock. 



With regard to its sight, prolonged and repeated experi- 

 ments have convinced mo that the animal possesses a share 

 of that faculty. A lighted match, brought within a foot of 

 the tank-wall in the dark, causes it to start violently and 

 then retreat instantly. Very different is its behaviour in 

 daylight towards an opaque object, such as a pencil brought 

 between it and the daylight and extended into the water. 

 Tiiere is sometimes a slight initial start ; but presently the 

 siphons bend so as to approach the object, evidently in 

 searcli of particles suitable for food. Tlie shadow of the 

 pencil is also noticed wjien the pencil lies outside the water, 

 but not so readily. Many hours, on many different days, 

 were spent in confirming these experiments, which were 

 repeated, with fresh sjiecimens, in three successive seasons. 



The sensitive and highly pigmented ends of the siphons 

 appear to form a pair of dark chambers, within which optical 

 impressions are received, through apertures which are per- 

 fectly round. This sight faculty in the siphon-ends is 

 eminently adapted to an animal which lives in a hole, with 

 only the siphons protruding. Barnea (^Pholas) Candida is 

 almost equally sensitive to light. Comparison was made 

 wit!i Lutraria elliptica, which po.ssesses si{)hons richly fringed 

 with cirri ; but here no such sensory faculty was found in 

 the siphons. 



The larval development I have as yet not been able to 

 trace beyond the very early stages, shortly subsequent to the 

 formation of the blastopore; but 1 hope to return to that 

 subject on a future occasion. 



EXPLANATION OF PLATE VIII. 



A & B. Zirphcea (Pholas) crispata, pier rocks, St. Andrews. Speci- 

 mens from the sandstone rock, to show the effects of friction during' 

 boring. The shells show worn places near the pedal end, where 



Ann. d) Mag. N. Hist. Ser. 8. Vol. ix. 25 



