collinge: on the anatomy of the genus myotesta. 15 



(14) which can best be likened to trowser buttons, which are concave 

 on one side. They are arranged on one base. Each disc has a 

 narrow central, cloven lumen, and arises out of cruciform muscle 

 fibres, of which the radiating bundles are enclosed. One might very 

 well imitate this structure, by dissecting out in large portions a number 

 of cross sections of the thick penis muscle and by placing them close 

 to each other upon a flat surface. It is this penis muscle which I 

 wished to bring into connection with the attraction and dart-glands of 

 the Vifrinae, which species together with others of the Atlantic 

 members of this genus, discharge upon themselves from the penis, and 

 must necessarily be more or less permeated by the seminal fluid. 

 Although it is quite certain that the lumenae of the discs must be 

 connected by a canal, I have as yet unfortunately failed to 

 distinguish any such Canal in the muscular tissue. The functions of 

 the organ are presumably the same as in other muscular penes. Still 

 we do not know precisely whether it performs the function of 

 discharging the spermatozoa, or whether it brings about impregnation 

 by some specialised fluid ; we can only conjecture that its function is of 

 some such nature judging from its form and structure." 



On reading the above description, I re-examined the material I 

 have, but was unable to trace the disc-like bodies. The retractor of 

 the penis, when carefully dissected aw^ay and teased, was similar to that 

 in other molluscs. Further, Dr. Simroth, is very definite in his 

 statement respecting the perforation of the mantle by the shell, he 

 u rites (p. 62) '"at the hinder end on the posterior of the [shell] sac, 

 somewhat to the left, a very fine cleft is observable, which cannot, 

 however, with certainty be traced as far as the opening of the mantle. 

 But tJie strildng peruJiarity is, that, through this deft, there jn-ojects 

 mitirard in the perfect snail, the fine point of the eonrh-lil:e shell* 

 The enclosed shell is composed of an anteriorly situated calcareous 

 plate, on which an extraordinarily, thin, wide, and structureless conch - 

 like shell fits close, and covers the sac." 



In Myotesta there is no conch-like shell, nothing beyond the flat, 

 plate-like shell, and this, in perfect specimens, is entirely covered and 

 enclosed by the mantle. 



Possibly Mi/otesta and Ostracolethe are distinct, but no doubt Dr. 

 Simroth will later give figures and a further description. 



I have to acknowledge with grateful thanks a grant from the 

 Royal Society, which has enabled me to obtain the material here 

 described and figured. 



* The italics are mine, W,E,C, 



