312 



NOTE ON A COLOUR MUTATION IN 

 HYALINIA HELVETICA Blum. 



By CHARLES OLDHAM. 



(Read before the Society, September 13th, 1911). 



Among some examples of Hyalmia helvetica that I collected at 

 Berkhamsted in March, 1910, was an adult which exhibited a very 

 unusual type of coloration. The shell was normally coloured, but 

 the animal was milk-white. It should not perhaps, strictly speaking, 

 be called an albino, but rather an instance of what Dr. H. Simroth 

 in describing an analogous condition in Vivipara vivipara (" Zoolo- 

 gischer Anzeiger," 1886. pp. 403-5) has termed " rothalbinismus," 

 for the whole of the body with the exception of the foot-sole and the 

 tentacles was sparsely and minutely freckled with red. The flecks 

 were barely perceptible on the head and neck, rather more apparent 

 on the tail and the sides of the foot, whilst at the edge of the mantle 

 arid around the pulmonary orifice, where in a normally coloured 

 animal there is a black collar, they were so numerous as to be almost 

 confluent. The eyes showed under a strong lens as faint reddish 

 specks. It may be that these minute red flecks are a normal con- 

 stituent in the coloration of H. helvetica^ and that they are quite 

 obscured by the darker pigment in a typically coloured animal. In 

 typical V. vivipara the red spots are apparent, and in the aberrant 

 animals described by Dr. Simroth they persisted, although all other 

 pigment was suppressed. It is perhaps something more than coin- 

 cidence that certain birds which have red in their plumage retain the 

 red when other pigment is absent ; white grey parrots usually have 

 red tails, and white bullfinches red breasts. 



BIBLIOGRAPHY. 



(limited to works received by the society's librarian). 



Manual of Conchology : Structural and Systematic. Second series.— A//- 

 monata, vol. xx. (parts 79 and 80), by H. A. Pilsbry, D.Sc. 

 The first half of this volume, viz., parts 77 and 78, has already been noticed 

 on page 74 of the current volume of the Journal. The two parts here reviewed 

 constitute a monograph of the genus Partula, which was constituted a family — 

 PartulidcE— by Pilsbry, in 1900. The species, which total in, are grouped geo- 



