36 AMERICAN JOURNAL 



the longitudinal diameter is parallel with the axis of the body. 

 This sac is situated on the left side, between the lung and the 

 renal organ. Several large vessels traverse the lung, and one 

 crosses it, and follows the median line of the gill. The smaller 

 vessels could not be traced, as the specimens had been many 

 years in spirits and were extremely rigid. 



Respiratory System. The lung resembles that of Auricula, 

 but is less developed than in that genus. It is rounded tri- 

 angular, and terminates in a multifid papilla, through which the 

 renal organ also discharges its secretions by a special duct. 



The branchiae are simply triangular folds of the lining mem- 

 brane of the mantle, somewhat attached to each other by a raphe, 

 in the line of which the principal vein passes. These folds are 

 more or less numerous in difierent individuals, apparently more 

 conspicuous in the older specimens, but by no means constant. 



Some authors have considered the lungs of mollusca as invagi- 

 nated gills. The present instance does not bear out the homology. 

 The gills are simple modifications of the mantle lining, while the 

 lung is a special organ, which serves a specified purpose, and 

 none other, and does not involve the mantle lining,^ except as one 

 of the membranes between which the lung is situated. 



Reproductive System. — The genitalia have a common opening 

 into a small papilla on the right side of the neck, behind the 

 head. The penis is very large and stout. It is contained in a 

 prcputium, consisting of two spirally coiled muscular layers. 

 These are continued in a kind of sac, which is reflexed anteri- 

 orly, and contains the testicle. The latter is very small and 

 ■easily overlooked, and the prostate is also inconspicuous. 



The ovary is large and kidney shaped. It is really doubled 

 ■up upon itself. There is a small spiral mucus gland at the pos- 

 terior extremity, but the duct of this gland is very long, and 

 ■only enters the oviduct beyond the ovary. The latter leaves 

 the ovary with a double flexure, and is prolonged as a simple, 

 slender tube entering the rounded-triangular uterus by the left 

 posterior angle. The genital bladder enters on the other side 

 by a short, stout tube. The former is rounded and transversely 

 ovate. The uterus is large and somewhat produced at the pos- 

 terior corners. The vagina, if we may term it so, is moderately 

 large, an-d opens into the genital papilla before mentioned. The 

 latter is very small in young examples. 



Nervous Si/stem. — This principally consists of a stout, ner- 

 vous collar, of ganglia united by nerve fibres, encircling the 

 ■oesophagus just behind the buccal mass. More numerous fibres 

 ■are given out below than above. One of the former connects 

 with a small accessory ganglion near the ovary. 



