210 MISS J. DONALD ON THE GENUS [May 1895, 



18. Notes on the Genus Murchisonia and its Allies ; with a Revi- 

 sion of the British Carboniferous Species, and Descriptions 

 of some New Forms. By Miss Jane Donald. (Communicated 

 by J. G. Goodchild, Esq., F.G.S. Bead February 20th, 1895.) 



[Plates VIII.-X.] 



I. The Subdivisions of the Genus Murchisonia and its Allies. 



In a previous paper J I gave an account of the establishment of the 

 genus Murchisonia by DArchiac and De Verneuil, and described its 

 characteristics. Since that date several new subdivisions of the 

 genus have been made by palaeontologists, and however reluctant 

 we may be to introduce new terms, we cannot well avoid doing so, 

 for many of the Murchison'm vary considerably from the type. 

 Palaeontologists differ both in the divisions that they adopt and also 

 in the value that they attach to them. AVhile some merely consider 

 these as sections, others regard them as subgenera, or even distinct 

 genera. Before proceeding to examine these divisions it may be 

 well to enumerate the generic characters of Munhisonia as now 

 defined : — 



Shell elongated, turreted, composed of more than six gradually 

 increasing whorls. "Whorls more or less angular, variously orna- 

 mented or smooth. Mouth oblong, oblique, terminated at the base 

 by a very short or truncated canal. Columella arched. In the 

 outer lip there is a narrow and more or less deep slit with parallel 

 edges, the successive filling-up of which during the growth of the 

 shell produces a continuous band throughout the whole length of 

 the spire. This band is distinctly defined, and composed of either 

 a single or double keel. Umbilicus open or closed. 



Though DArchiac and De Yerneuil do not indicate any par- 

 ticular species as type, the first mentioned on the list that they give 

 has generally been accepted as such, namely, M. sjnnosa, Goldf. 

 Mr. Yv hidborne 2 has since shown that this shell is identical with 

 M. turbinata, Schlot., and that it is very variable in shape and 

 ornamentation. Some individuals are elongated, others are short 

 and buccinoid ; the whorls may be flattened, slightly convex, or 

 decidedly angular. They are generally ornamented by rows of 

 tubercles, but there are numerous intermediate forms showing 

 varying degrees of tuberculation, and merging into perfectly smooth 

 forms. The sinual band is grooved, bounded by two prominent 

 keels, and situated on the angle or widest part of the whorl. I 

 have had the privilege of examining the numerous varieties of this 

 species in the collection of Mr. Yicary, who also kindly gave me 



1 ' Notes upon some Carb. Sp. of Murchisonia in our Public Museums,' Quart. 

 Journ. Geol. Soc. vol. xliii. (1887) p. 617. 



2 ' Monogr. Devon. Fauna of the South of England,' part iv. Paheont. Soc. 

 1892, p. 306. 



