HELIX. 253 



very peculiar in Vallonia and Strobila, in being very low and wide, and having 

 numerous cutting points, quite resembling those of Pupa. In Mesodon, Trio- 

 dopsis, and Arionla, the marginals are longer than wide, with only two, some- 

 times bifid cutting points. In Stenotrema and Polygyra they are rather wider 

 than long, also with two more bluntly bifid cutting points. It must be borne in 

 mind, however, that my observations have not led me to believe these charac- 

 ters sufficiently constant to be of generic value. There is also some variation 

 in the mode of passing from lateral to marginal teeth, even in the same genus ; 

 in some cases the transition being made simply by a gradual modification of 

 form, in others by the splitting of the inner cutting point. These points will 

 be treated more fully under each genus. 



Descriptions of the genitalia of each species observed are given below. A 

 few general remarks are here added on the general arrangement of the organs 

 in the group of genera formerly known as Helix, including even the Zonites, 

 for the purpose of more convenient comparison. 



The testicle, very unlike that of slugs, is imbedded or commingled with the 

 parenchyma of the posterior or superior lobe of the liver; and, instead of hav- 

 ing an aciniform appearance, it is composed of fasciculi of short caeca. It is 

 usually of a lighter color than the liver. The epididymis is long, and generally 

 very much convoluted, and contains a white, silky, tenacious substance, often 

 distending the tube to a considerable degree, composed of spermatozoa. At 

 its junction with the prostate gland, it always receives the duct of a small acces- 

 sory gland, composed in different species of Helix, of from three to nine acini. 



The prostate gland is generally larger than in the Limaces. 



The vas deferens generally corresponds in length with the curve passing 

 from the termination of the prostate gland downwards to the cloaca, and thence 

 to the summit of the penis. Generally, it is a white, narrow, cylindrical, fre- 

 quently undulated tube. Sometimes it is distinctly and strongly muscular. In 

 some species at its commencement it presents a dilated and glandular appear- 

 ance. In Patula solitaria it is much dilated, annulated, and glandular at its 

 termination. In most instances it joins the summit of the penis sac ; in some, 

 however, it joins the penis sac at the side, very near the summit. 



The penis sac varies very much in form and size ; most usually it partakes 

 of a conico-cylindroid form. In some species it is very large and long, cylin- 

 drical, collapsed, and flaccid. In others it is long, clavate, and bipartite at the 

 summit, or it is short, stout, and clavate. In many species it has a thick, pre- 

 putial membrane, originating around its base, and rising upwards so as to 

 envelop it for one or two thirds of its extent. In M. profunda the base of the 

 penis protrudes into a sheath joining the cloaca, in the form of a cone with its 

 apex bent upon itself. In Z. suppressus, it is wholly enveloped in a sheath 

 derived from a tubular offset from the duet of the generative bladder. 



The muscular tunic of the penis is thick and strong. The internal lining 

 mucous membrane usually presents a number of large rugae, longitudinal and 



