1858.] MUHCHISON XOETHERN HIGHLANDS, ETC. 379 ' 



tion is 3-25 to 2. This difference is probably in exact accordance 

 with a less favourable nature of the locality, which did not permit 

 of rapid growth or the attainment of full size. 



OjpMleta levata, Vanuxem, besides being a small species, has more 

 numerous whorls, and appears to have a narrower umbilicus. 



EuoMPHALTJS (Macltjiiea) matutinus. Hall ? 

 (Palaeont. New York, vol. i. pi. 3. %. 3.) 



Several small specimens in the Durness limestone appear to cor- 

 respond with the species which accompanies 0. comjpacta in Canada ; 

 but no stress should be laid on the identification of so obscure a 

 fossil ; it may be a representative form only. Another and some- 

 what larger species is found with it. There is, besides, a large 

 Raphistoma, like B. lahiata, Emmons, and scarcely distinguishable 

 from it. 



Pleitrotomaria Thule, spec. nov. PL XIII. fig. 13. 



P. vix unciam lata, pyramidata (ad apicem 45°), suturis inconspicuis ; carina 

 prominula, angusta, subplana; anfractibus 5-6, striis supra obscuris, infra 

 profundis exaratis ; basi subplana, ore rhomboideo. 



About five lines high, and the same breadth at base, of a pyra- 

 midal shape, the five or six whorls regularly conical, and scarcely 

 distinct at the sutures except by the prominent narrow band. The 

 whorls are nearly smooth above the band, or crossed only by very 

 oblique curved Imes of growth ; but below the band they are very 

 rough and prominent over the nearly plane base. The band itself 

 is rather prominent, angular above and below, but with no depres- 

 sions or keels upon its surface ; it is crossed by strong arched Hnes 

 of growth. The mouth appears to be regularly rhomboidal. 



Many palaeozoic species resemble, yet are not identical with, this 

 shell. It is only necessary to compare it with one allied species, to 

 which at first sight it is likely to be referred, the P. suhconica of 

 Hall's ' Palaeontology,' vol. i. pi. 37. fig. 13. That species, however, 

 as figured, has a much more prominent and rather ventricose base, 

 and is moreover transversely and closely striated, the striaB on the 

 keel being collected into two distinct ridges, which margin the keel 

 and make it almost a double one. There is nothing of this in our 

 species, which has also more numerous whorls. If Hall's figures 

 Sd, 8e, be of the same species, the resemblance is closer ; but these 

 are only internal casts ; and his fig. 8 « is evidently the type 

 specimen. 



Four specimens, of which two are figured, occur near Balnakill 

 in Durness. 



Mtjrchisonia (Houmotoma*) gbacilis, HaU ; var. geacillima. 

 PI. XIII. figs. 7, 8. 

 (Palaeont. New York, vol. i. pl. 39. fig. 4. M. angustata, op. cit. pi 10. fig. 2.) 

 It is not certain that this form is identical with those given by 



* Proposed in 'Decade I., Q-eol. Survey Canada ' for the elongate beaded forms 

 of Murckisonia. 



