600 K. ETHERIDGE ON THE PALAEONTOLOGY OE THE 



the Polar area ; that they must have been very different, so far as 

 the Laniellibranchiata are concerned, during the deposition of the 

 Carboniferous and Silurian rocks appears evident, for we find none. 



Class GASTEROPODA. 



Very few species of this class have been collected, and with one 

 or two exceptions all are small species — not that they are dwarfed 

 forms through low temperature or paucity of food or other causes ; 

 the whole group seems to be poorly represented, so far as the collec- 

 tions made are any test. Large species of the genus Murchisonia, 

 one or two Locconemce, and species of Macrocheilus and Holopella, 

 JRliaphistoma or Euomphalus, Acroculia, and Platyceras seem to be all 

 that occur in the collection. Amongst the Carboniferous-limestone 

 series not a species occurs. It is seldom that Gasteropoda and Bra- 

 chiopoda are associated together, and in the Carboniferous series they 

 are mostly of the latter class ; hence, perhaps, the horizons collected 

 from were not favourable to the Gasteropoda during their deposition. 

 I can hardly imagine a great paucity of species in this class in these 

 Upper Silurian rocks, considering that the bathymetrical conditions 

 must have been favourable to their life, development, and distribution. 



Considering the fauna of the Silurian rocks of North America and 

 Canada, as well as that of our own country, from rocks of the same 

 age, associated as they are with a similar assemblage of Coelen- 

 terata, Crustacea, and Brachiopoda, we should expect to find 

 more species. Doubtless the difficulty in collecting was great, hori- 

 zontal extension, or space, and vertical distribution, or time, being 

 two elements in the collecting not easily realized under the 

 adverse climatal circumstances and other difficulties attending such 

 an expedition ; for it could only have been from the faces of the cliffs 

 where the beds were exposed that fossils could be obtained in situ. 

 As regards Post-Tertiary species, very few of this class occur in the 

 living molluscan fauna of the Polar area, Troclius umbilicatus, T. 

 olivaceus, and Oylichna striata being amongst the chief species. The 

 last-named delicate shell (C?/^c7ma striata) occurs in a fossil state at 

 Spitzbergen and in the Clyde beds, as well as in the State of Maine. 

 Tricliotropis borealis, Pleurotoma Trevelyana, Trophon clatliratum, 

 and Buccinum tenue are the chief forms of Gasteropoda in the Post- 

 Tertiary deposits ; but none came home in the Carboniferous collec- 

 tion. 



Genus Murchisonia, D'Archiac and DeVerneuil, 1841. 

 Murchisonia latifasciata, Ether. (PI. XXYII. fig. 1.) 



Fortunately we have a small portion of the shell on this single 

 specimen which shows enough structure to enable me to say that I 

 know no shell like it, or rather cannot find either description or 

 figure that agrees with it. These shells, which resemble elongated 

 Pleurotomarice, are at all times difficult to determine : in the present 

 case we have only two whorls, the body-whorl and that adjoining; 



