Cyclostrema, Adeorbis, Vitrinella, and related genera. 103 



defined the genus and figured A. suhcarinatns (Mont.) as an exam- 

 ple, placing it next to Cyclostrema. 



Chenu, in 1859, defined the genus, mentioning and figuring A. 

 subcarinatus (Montagu) as an example, adding also figures of A. 

 striatiis Wood. 



Mr. Jeffreys, in 1865, seems to have been the first author to make 

 any generic distinction between the several sj)ecies of Wood. In 

 "British Conchology," vol. iii, p. 315, he described as Trochus 

 Duminyi Requien, a recent shell found at Bonegal Bay, identifying 

 it as Delphinula Duminyi Requien, 1848 = Adeorbis striatus Wood, 

 1848 = Valvataf striata Philippi, 1836, and mentioning A. supran- 

 itidiis Wood, and A. tricarinatus Wood, as fossil varieties. The 

 specific name striata had been preoccupied by Trochus striata Linn^. 

 He made a special section under the genus Trochus for the reception 

 of such forms, as " they are very distinct from the typical Adeorbis 

 subcarinatus (Montagu), the operculum of which is paucispiral and 

 horny, with lateral nucleus." The section is defined as follows : 



" C. Very small, circular, nearly flat-spired with exceedingly 

 wide and open umbilicus. Circulus.'''' See p. 110. 



He mentioned that the animal of Duminyi is unknown, but de- 

 scribed the operculum as follows : 



" Operculum circular with about a dozen volutions which wind 

 spirally and gradually and converge to the centre." A very poor 

 figure of the species is given in vol. v, pi. 62, fig. 5. 



Fischer, in his " Manuel de Conchyliologie," defined Adeorbis^ 

 and stated that the operculum is horny, spiral and excentric, giving 

 and figuring A. subcarinatus as the type. 



Tryon, in his "Manual of Conchology," 1883, defined the genus, 

 mentioning and figuring A. subcarinatus (Mont.) as an example, but 

 stated that the operculum is " shelly, subspiral." 



There is little doubt that Wood intended A. striatus to stand as 

 the type, but, as he included three quite distinct forms in the genus 

 and failed to mention a type species, according to definite rules of 

 nomenclature, the type given by the author who first separates the 

 species of the genus has to stand as the one to be adopted. 



A. subcarinatus (Mont.), of which I have several examples (No. 9428) 

 before me, collected at Guernsey, England, and presented to the 

 Museum by the Rev. Canon A. M. Norman, is a very small (the larg- 

 est is about 2 •5""^' in diameter), moderately thick, white shell, of 

 about three abruptly enlarging whorls, so coiled that the suture ends 

 at the periphery of the preceding whorl. The whorls are well 



