260 MISS JANE DONALD ON THE GENEEA [^J^ay 1 899, 



whorls appear more angular and the form of the band is different. 

 The three latter species are distinguished from Hormotoma by having 

 a prominent band, but are evidently closely allied, as the lines of 

 growth agree in curving backward and forward very obliquely ; and 

 in adult specimens of M. attenuata, near the aperture, the lines of 

 growth may be traced from suture to suture, passing over the band 

 where they are strongly arched, but there is no break as in the typical 

 Murchisonice. It may here be mentioned that Pleurotomaria insignis^ 

 Eichw.,M hough of much greater size than the type of Bormotomcf, 

 agrees with it in all essential characteristics. The band is usually 

 level with, or but slightly depressed below, the surface of the whorj, 

 though sometimes in the adult it becomes rather elevated ; the lines of 

 growth, however, continue from suture to suture, as on the rest of 

 the shell. There is thus a connecting link between the members of 

 Hormotoma that have a flat, slightly margined band, and those forms 

 where the band is solid and elevated throughout all the whorls. 

 This latter group occurs also in America, and is represented by 

 M. Artemisia, Billings,^ from the Calciferous Eormatiou. It would 

 perhaps be more advisable to class it as a sub-genus of Hormotoma, 

 rather than include it in that genus, or regard it as representing a 

 distinct genus itself. 



Eichwald records Pleurotomaria insignis^^ichw., PI. exilis, Eichw., 

 PI. bellicincta, Hall, and PZ. cingulata, ILis., from the Ordovician and 

 Silurian of the Baltic Provinces and the Urals. The first has since 

 been more fully described and figured by Koken, who kindly allowed 

 me to examine his specimens at Tubingen, and for reasons previously 

 given I refer it to the genus under discussion. Koken ^ considers 

 that PI. exilis may possibly be a young example of this species. He 

 also states that Eichwald has described several distinct forms as 

 PI. bellicincta, Hall, one of which from Hohenholm is more slender, 

 and Koken '' designates it Eftomaria Mrnaensis, while others he 

 believes to be allied to Murchisonia Milleri, Hall, One specimen is 

 compared with Turbo cin-osus, Sow., by Eichwald. Schmidt ^ says 

 that the shell from Wesenberg called PL bellicincta, Hall, by Eichwald 

 is perhaps identical with P?. insignis, Eichw.; Eichwald, however, 

 states that it is one half smaller than that species. He records 

 PI. cingulata, His., from both the Upper Stage of the Urals and the 

 Lower Stage of Esthonia. This species is essentially an (Upper) 

 Silurian form ; it is, therefore, doubtful whether the shells from the 

 latter locality are really Hisinger's species. Koken considers them 

 distinct and names them M. Eicliwaldi.^ The examples from the 

 Urals are much larger : that figured is evidently different from 



1 ' Leth. E08S.' vol. i, pt. ii (1860) p. 1164 & pi. xliii, fig. 1. 



2 Geol. Surv. Can. ' Pal. Foss.' vol. i (1865) p. 345 & fig. 332. 



3 ' Die Gastrop. des Bait. Untersilurs,' Bull. Acad. Imp. Sci. St. Petersb, 

 ser. 5. vol. vii (1897) no. 2, p. 207. ^ Ibid. p. 208. 



•' ' Untersuch. iiber die Silur. Form. v. Ehstlaud, Nord-Livland u. CEsel,' 

 Archiv IS'aturk. Liv-, Ebst- u. Kurlands, ser. 1, vol. ii (1858) p. 202. 



^ ' Ueber die Entwickelung der Gastropoden vom Cambriutn bis zur Trias,' 

 Neues Jahrb. Beilage-Band vi (1889) p. 371. 



