114 PEOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



ON THE GENUS ACAVUS, Mont. 



By E. R. Stkes, B.A., F.L.S., etc. 



Read 6th April, 1900. 



The genus Acavus was founded by Montfort (1810) for the Helix 

 hcemastoma of Linnaeus. This species was subsequently included by 

 Schumacher in his Otala. In 1887 Mons. Ancey proposed Oligospira 

 for A. Walton i and A. Skinneri ; of this group or subgenus Acavellu, 

 Jousseauine (Mem. Soc. Zool. France, torn, vii, 1894, p. 288) is 

 a synonym. 



The following arrangement is based purely on conchological grounds, 

 and was formed without any knowledge of the anatomy of members of 

 the genus as set forth in the preceding paper by Mr. W. B. Randies, 

 so that it is of great interest to compare our several conclusions. 

 It has not been thought necessary to reproduce the references already 

 given by Mr. Pilsbry in the " Manual of Conchology." 



1. AcA'vtrs h^iiastomus (Linn.) is an exceedingly variable shell in 

 colour, and a convenient arrangement of the varieties known to me 

 may be made by noting the colour of the lip. 



(«) Red lipped. The banding varies from a very dark to pale 

 chestnut colour, and the number and position of the bands may 

 be traced from the almost unicolorous shell with confluent 

 bands to one in which a very narrow band is seen below the 

 suture and another encircling the umbilical area. I have never 

 seen an absolutely white specimen with a red lip. The variety 

 concolor, Pilsbry, belongs to this group. 



(J) Black-lipped. Similar remarks apply to this form, the Helix 

 melanotragus of Born. Dr. von Martens has kindly pointed out 

 to me the following interesting point, namely, that there are 

 ' band-formations ' characteristic of the red- and black-lipped 

 forms. The most common varieties of the former are 12305 

 and (123)05, while that of the latter is 1(23)05. 



(c) Purple-, or lilac-lipped. The var. conus, Pilsbry. Of this I 

 have only handled a single specimen, and it is, I believe, rare. 



{d) Particoloured Up. Two specimens, with the lip half black, 

 half white (tinged with brown), corresponding to the position 

 of the bands. Formula, 1(23)05 and (123)05. 



Mr. Pilsbry quotes Benson for {inter alia) the fact that the shell is 

 covered with "green foecula": on a specimen sent to Kew Gardens 

 this green covering was determined to be an alga very closely allied to 

 Pleurococcus mucosus, Kntz. 



2. Acavus peosperus (Albcrs). I strongly suspect that this will 

 prove to be only a variety of the last species ; the type is in the 

 Berlin Museum. 



