52 JOURNAL OF CONCHOLOGY, VOL. I4, NO. 2, APRIL, I913. 



Linne's laws of scientific nomenclature — 'Idiotse imposuere nomina 

 absurda.'" The Rev. Frank Knight, however, suggests very plausibly 

 that Leach called it after a great oriental scholar the Abbe Simon 

 Assemani, who died in 182 1 at Padua, Leach being in North Italy in 

 the same year— contains but the one estuarine species grayana, so 

 named by Leach in honour of Dr. Gray, of the British Museum. 



The family Fomatiidce has in England but one species, better 

 known as Cyclostoma. The name is derived from the Greek Trwjua, a 

 cover, i.e. here an operculum. Its var. mariiioi-ea has marble-like 

 markings and is free from striation ; its var. ochroleuca is whitish- 

 yellow. 



The family AcicuIidcB {acicula a hair pin — the priniccval straight and 

 white bone pin being in mind) contains only the very minute A. 

 litieafa, lined or striated in the line of growth. 



The family of Neritidce has with us but one genus Neritina and one 

 section of that genus, Theodoxia, and one species, y7«w«//7/V. Nerita 

 is the name given by Pliny to a sea-shell, which Smith's Latin 

 Dictionary describes as "a sea-muscle {sic) resembling the nautilus" ! 

 The word is originally Greek and probably derived from Nereus, the 

 sea-god. Its var. cerina is named from ceriim wax, as being ) ellow. 



Passing now to bivalves or Pehcypoda (axe-footed, from the sup- 

 posed resemblance of the protruded foot to an axe) the group to 

 which all our British species belong is that of the Eulaineliibriuichiata, 

 i.e. having well laminated branchiae or gill plates. Our fluviatile 

 bivalves also belong to the division Subi/iytilacecE or connections of 

 the Mytilus or mussel. 



The name of the genus Dreissensia was originally Dreissena. The 

 origin of the name is the commemoration of M. Dreissens, a druggist 

 of Mazeyth, a place in Holland. Our only species is called poly- 

 inorpha or many shaped. It has a var. angusta (narrow) and a var. 

 dilatata (broadened) and these practically comprise all the variations 

 of form. 



The family Unionidx derives its name from Unio, a pearl, because 

 British pearls have for ages been chiefly obtained from a U7iio. The 

 species pictoruni, " the painter's mussel " (or, as in Gray's Turton "the 

 thin painter's Utfion") is so named because sometimes gold and silver 

 paint was sold in the shells for illuminating work. It has a var. 

 iiifvirostris, i.e. with curved beaks ; another latior, i.e. broader than 

 usual ; another radiata, i.e. with yellow and green radiations ; and 

 :ix\oih&v platyrhyjichoidea, i.e. in form like Unto platyrhynchus (hxosid 

 nosed) of Rossmassler found in S.AV. Austria. Ufii'o tumidus (swollen) 

 is broader and thicker than the preceding species. Its var. nuilleri, 

 named after the Danish naturalist of the eighteenth century, is more 



