MAUGIXAL PROCESSES IX SHELLS. 1061 



The way in wliioh these processes protect the lamellibranch 

 lias yet to be explained. From actual and repeated observation 

 one would expect that the prosobranch could extend its proboscis 

 for a short distance and insert it amongst the processes, which 

 are not genei-ally very near together, and so drill its hole without 

 trouble. It is, however, necessary for the Murex to obtain a 

 very firm hold with its foot before it can operate its drill, and 

 one finds cases where a distinct impression of the foot has been 

 made among the growths on the shell before any damage has 

 been done at all. The point of special interest to the naturalist 

 as well as to the practical pearl-fisher, is that one cannot estimate 

 the damnge done by Murex by counting how many of a lot of 

 dead shells have tlie characteristic hole drilled through them. 

 In more than three cases out of four no hole is drilled at all, 

 Murex having found an easier way. It finds the flexible edge of 

 the shell, then by contractions of its foot breaks a piece away. 

 The mucus of the foot-glands is then poured out in quantities, 

 and this has some poisonous effect, as the animal, while still 

 untouched, ceases to respond to the stimuli which ordinarily 

 cause a smart closure of the shell. The abundant flesh of this 

 species is all devoured before putrefaction sets in. 



EXPLANATION OP PLATE LX. 



Except for fis's. 6 and 7, speeinieii-i of about the same aij-e liave been drawn to the 

 same scale, the age being souicthiui;' under six inontlis, the magnification X3. 



Fig. 1. Cliama-foliata. A dead shell, widely gaping, seen from above, i. e. from 



anterior end. a. hinge ; b, ventral edges of shell. 



The shell-processes are seen \o be about half tlie diameter of the shell in 



length. At- this age they and the shell are brilliantly coloured with dark 



red bands on a light yellow ground. In the adult shell the processes 



remain conspicuous (hence the s))eciHc name), but in the young they are 



out of all proportion to the size of the animal that forms them. 

 Fig. 2. Upper valve only of Chama sp. ? Shell red, processes white. In adult shells 



processes quite inconspicuous, generally absent. Animal then protected by 



the extreme solidity of its shell. 

 Fig. 3. SpnndyJus sp. ? A specimen which is beginning to take the adult shape 



and to form the characteristic strong spatulate processes instead of the 



brittle needle-like serrated pi-ocesses characteristic of the younger stages. 



These seriulations are .shown in only a few instances in the figure. 

 Fig. 4. A rather younger specimen of the same, with long slender processes only and 



edge of shell serrated. Upper valve only drawn. 

 Fig. 5. Margaritifera margarltifera. A specimen 12 mm. across shell, with 



])rocesses 7 mm. long. Probably three months old ; younger specimens 



than this have perfectly smooth shells like the umbonal region of the 



present si^ecimeu. 

 Fig. 6. The same, X2, aged about 7 months. Showing development of proces.ses 



characteristic of the first two or three years' growth. Some of the radial 



rows of processes are thick and spatulate; others, which are thinner, shrivel 



and become pointed, as in the figure, on drying. 

 Fig. 7. The same. Part of the edge of a three-year old shell which has grown slowly. 



Sliells more rapidly developed are distinguished by the wider spacing 



of the processes. 



Proc. Zool. Soc— 1911, No. LXXII. 72 



