Mr Etheridge on a Small Naticiform Gasteropod. 167 



thin, not reflected ; columellar or inner lip not reflected, but 

 twisted or spirally grooved within. Umbilicus none. 



Naticopsis, according to the original description,* differs from 

 the typical Natica, in the absence of an umbilicus, and in the 

 presence of a peculiar operculum and flattened columella. In 

 an amended description,^- published in 1853, Professor M'Coy 

 modified his previous definition by stating that a "minute um- 

 bihcus only visible in the casts " existed. Practically, this 

 reduces the dissimilarity between Natica and Naticopsis to the 

 presence of the concentric instead of spiral operculum of the 

 former, and the flattened columella. My own impression is that 

 Professor M'Coy is right in both his descriptions ; in other 

 words, in young forms of Naticopsis, or perhaps even in some 

 species, the umbilicus may be visible ; in others, on the con- 

 trary, hid by the inner lip, which is usually reflected to a 

 greater or less extent. 



Writing still more recently, the eminent American Palaeon- 

 tologists, Messrs Meek and Worthen, point out \ that, whether 

 Naticopsis be umbilicate or not, its separation from Natica is 

 ensured by the condition of the operculum. In the latter it 

 has a spiral structure, but in Naticopsis the operculum accord- 

 ing to the above authorities is thick and shelly, oval or sub- 

 circular in form, with a lateral or sub- marginal nucleus, and 

 shows not the slightest traces of the spiral or sub-spiral 

 structure, and articulating projection of the Neritidce. On the 

 inner side the operculum of Naticopsis shows a distinct uni- 

 form scar of attachment, and on the outside the fine, but dis- 

 tinctly concentric, lines of growth. The Geological collection 

 of the British Museum contains a very fine example of Nati- 

 copsis elliptica (Phill. sp. T), with the operculum in place, and 

 I am able in consequence to confirm many of the preceding 

 observations made by Meek and Worthen. As before stated, 

 the little shells now under consideration were formerly re- 

 ferred by me to the genus Littorina, but from wretched mate- 

 rials. A study of Mr Bennie's recent gatherings, which I be- 



* Synop. Carb. Lime Foss., Ireland, 1844, jp. 33. 



+ Brit. Pal. Foss., pp. 301 and 543. 



X Illinois Geol. Survey Keport, ii., p. 364. 



