130 Mr. L. Reeve on the recent Orbiculse. 



on the roads (O. ostreoides), is supposed to be a native of the 

 shores of North or West Africa ; and there is a small species 

 (O. Stella) in the Eastern Seas. The rest are inhabitants of the 

 New World, where Crania is unknown. O. stella has an ana- 

 logue in the West Indies in O. Antillarumf and an allied repre- 

 sentative, of more solid growth, in O. Cumingiij which ranges 

 along the western coast of America, from Peru to Guatemala, 

 and reaches to Mazatlan. The most striking type of the genus 

 is that represented by three species on the coast of Peru, but 

 not extending northward to Central America — P. lamellosa, 

 lavis, and tenuis, of the last of which Mr. Cuming possesses 

 specimens, strange to say, from South Australia. 



Synopsis of Species. 



1. Orbicula ostreoides, Lamarck, Anim. sans Vert. 1819, vol. vi. 

 part 2. p. 237. 



Discina ostreoides, Lamarck. 



Orbicula Norvegica, Sowerby, in Linn. Trans. 1822 (not of Lamarck). 



Orbicula striata, Sowerby, in Thes. Conch. 1846. 



Crania radiosa, Gould. 



Orbicula Evansii, Davidson. 



Hab, North-west Africa ? (in crevices of brown oxide of iron). 



This species was originally named Discina ostreoides by La- 

 marck, from a specimen sent to him, in 1819, by Mr. James 

 Sowerby, father of Mr. G. B. Sowerby, sen., who described it 

 the following year, in a paper read before the Linnean Society 

 (but not published until 1822), as Orbicula Norvegica. He had 

 discovered it in abundance in the crevices of a quantity of ballast 

 stone (brown oxide of iron) used in the neighbourhood of Lam- 

 beth for mending the roads. Mr. Sowerby makes no mention 

 in his monograph, published twenty-four years later in his son's 

 ' Thesaurus Conchyliorum,' of having described this species as 

 O. Norvegica, but names it for the first time O. striata, although 

 he bears testimony to its being the species on which Lamarck 

 founded his genus Discina. 



I am of opinion that Mr. Davidson's O. Evansii is a specimen 

 of O. ostreoides in which the vertex of the upper valve and corre- 

 sponding disk of the lower valve are more central than usual, 

 owing to the shell's position of attachment in the hollow grooved 

 crevice of the iron-stone ; and the lower valve is more convex for 

 the same reason. The type-specimen of O. Evansii is exactly 

 like distorted specimens of O. ostreoides jammed within the 

 crevices of the iron-stone. At first I fancied that the habitat 

 Bodegas, California, given by Mr. Davidson for O. Evansii, on 

 the authority of Mr. Cuming, might be a mistake ; but it may 

 be remembered by those who have studied the phenomena of 



