276 GLLBERT C. BOURNb]. 



pericardial aperture is the representative of the left auricle, 

 and if we regard all that vessel as auricle which is covered 

 with pericardial glandular tissue^ his suggestion is correct. 

 But as the muscular coat of the afferent vessels of the heart 

 does not extend as far in Enigma as in An o mi a, and as 

 the left afferent vessel divides close below the intestine into 

 an anterior and a posterior vessel^ I have preferred to restrict 

 the term auricle to those muscular vessels which embrace the 

 intestine. 



The gonads. — The sexes are separate. The ovaries and 

 testes occupy the same position in the two sexes, so a descrip- 

 tion of one will apply equally well to the other. The left 

 gonad is much the larger of the two, and extends for a long 

 distance in front of and behind the gonopore. Its anterior 

 moiety has the same relations as in Anomia, that is to say, 

 it runs forward below the stomach and liver, and just above 

 and to the right of the left labial groove to the mouth, 

 where it passes to the right of the attachment of the anterior 

 retractor pedis muscle, and passing into the mantle forms 

 the large prteoral mass which is so conspicuous a feature 

 when the animal is opened. The posterior moiety runs back 

 as a fine canal, bearing a few slightly branched diverticula, 

 below the Ccecnm of the crystalline style and above the 

 byssus muscle; its course being here on the right rather 

 than on the left side of the body. Behind the byssus muscle 

 it passes over to the left side of tlie body, and divides into 

 two branches running respectively along the upper and lower 

 edges of the posterior retractor pedis muscle. Behind the 

 attachment of this muscle the gonad passes into the left 

 mantle lobe, and there forms a large follicular mass extend- 

 ing back for some distance beyond the level of the anus, as 

 shown in figs. 2, 12, 13. The left gonad does not extend 

 into the mantle in Auomia, and Pelseneer (14) has stated 

 that it does not do so in any of the Anomiacea, a somewhat 

 rash generalisation which must now be corrected. The right 

 gonad in the anterior part of its course lies dorsad of the 

 stomach and liver on the upper side of the visceral mass, 



