129 



and have personally examined specimens in the British Museum, 

 the Museum of Practical Geology, the Museum of the Geological 

 Society, the Woodwardian Museum, the Museum of the Geological 

 Survey of Scotland, as well as other pubhc collections located at 

 York, Liverpool, Leeds, &c. Mr. John Young, of the Hunterian 

 Museum, Glasgow, has been most kind, both in allowing me to 

 study his private collection, and in giving me specimens to com- 

 pare with my own. 



Most of the shells whose description follows, have been at one 

 time or another described under the generic name of Murchisonia. 

 In many instances it is clear that this identification has been 

 founded upon error. 



In 1841, Viscount D'Archiac and M. E. de Verneuil {Bulletin de 

 la Soc. Geol. de France, t. xii. p. 154,) gave the name of Murchi- 

 sonia to a group of elongated shells of which the outer lip is 

 notched, and the mouth is effuse below. Subsequently, Salter, in 

 1859, {Geol. Survey of Catiada, Dec. i, p. 18,) distinguishes from the 

 true Murchisonice a group of beaded shells having the outer lip 

 notched, but with the mouth rounded and not effuse below. To these 

 he gives the name Hormotoma; and H. gracilis, a Silurian form, may 

 be taken as the type. There is another group of shells bearing 

 considerable external resemblance to Murchisonia, to which Messrs. 

 Meek and Worthen in 1861 ( Proc. Acad. Nat. Sci. Phil. p. 146,^ 

 have given the name Orthonema. These shells are elongated, and 

 they are generally ornamented with keels ; but the outer lip is 

 straight and is not notched; hence the lines of growth come 

 straight down the whorls without any trace of the deep sinus 

 characteristic of the true Murchisonice. Some small elongated 

 beaded shells, ornamented with keels, or with rows of tubercles, 

 were sometimes included in the genus Murchisonia, and at other 

 times were referred to Loxonema, Turritella, Aclis, Turbonilla, etc. 

 These shells M. de Koninck {Annales du Musee Royal UHistoire 

 Naturelle de Belgique, T. vi. 3me Partie, p. 86, 1881,) now groups 

 under the generic name of Aclisina. In this genus the mouth 

 is oval, and the outer lip is entire, instead of being notched as it 

 is in Murchisonia. 



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