60 Proceedi7itjs of the lloyal Physical Society. 



account, together with the structure of the operculum, it is 

 more than probable that the genus is distinct from its ally, 

 Natica. On the whole, I think with Messrs Meek and 

 Worthen, " it will be found to be the type of an extinct 

 family, Naticopsidae, near the Naticidse."* A very useful 

 subdivision of Naticopsis has been introduced by the same 

 enthusiastic Palaeontologists, under the name of Trachy- 

 clom%a,-\ to include such shells as Buccimcm hreve (Sby.), in 

 which the shell is ornamented with small nodes. So far as 

 I am aware, this species has not been met with in Scotch 

 Carboniferous rocks. A new species has lately been de- 

 scribed by Messrs Armstrong and Young (iV. Bohroystonensis), 

 with prominent semiarcuate costulae, but this character 

 appears hardly sufficient to bring it within Trachydomia. 

 A re-distribution of the shells now referred to Ncdicopsis is 

 requisite before a satisfactory arrangement can be arrived at. 

 This has to a certain extent been effected by Professor de 

 Koninck, in his recently published fine work, by the intro- 

 duction of two additional genera for species formerly placed 

 in Naticopsis. In the first of these, NatiTia,\ is placed a 

 handsome shell, known as Natica lirata (Phillips), easily 

 distinguished by the longitudinal lamellee of the surface, from 

 the other Carboniferous so-called Naticas, that the wonder is 

 it has remained so long unrelegated. The species is met with 

 sparingly in Scotland, for instance, at Arden, near Thornlie- 

 bank. 



The second genus Tychonia^ is proposed by de Koninck 

 to receive another aberrant Carboniferous Naticopsis, the N. 

 Omaliana (De Kon.), again a Scotch species. There is no trace 

 of a callosity upon the return of the spire, as in other Natieopsis. 



Omitting the two foregoing species the number now apper- 

 taining to Natieo^jsis found in Scotland is six, or adding Mr J. 

 Young's last determination of N. talulata,\\ seven in all. 



AVe now approach three shells closely allied to one another, 



* Illinois Geol. lleport, ii., p. 365. t Ibid., p. 364. 



X Fauiie du Gale, Carbonif., Gasteropodes, p. 5. § Ibid., p. 8. 



II " Notes on the genera of Gasteropod Mollusca from the Carboniferous 

 Limestone Series of the Central and West of Scotland" (Trans. Geol. Soc, 

 Glasgow, 1881, iv., pt. 1, p]). 85-93— sec p. 87). 



