568 MISS J. DONALD OF NEW AND LITTLE-KNOWN 



most keel. Lines of growth distinct and slightly irregular in 

 strength, curving backwards to the band above and forwards below ; 

 strongly arched on the band, the greatest convexity being nearer 

 the upper keel than the lower. Sutures prominent. Mouth im- 

 perfectly preserved, probably somewhat rounded. 



This shell bears so strong a resemblance to M. conula, De Kon., 

 that I consider it a variety of that species. It agrees with it in 

 the form of the whorls, the number and position of the keels and 

 the flatness of the base. But it differs in having a smaller spiral 

 angle than the specimen figured and described by De Koninck. De 

 Koninck also states that the sinus is between the two strongest 

 keels instead of above. On the specimens, however, that I have seen 

 both in the Brussels Museum and in the British Museum (Natural 

 History) from Vise the lines of growth appear to indicate the sinus 

 as being above the angle, precisely as in the British shells. Most of 

 the Belgian specimens are imperfect and compressed, so that it is 

 difficult to ascertain the spiral angle with accuracy. The upper 

 part of the spire increases more rapidly than the lower, and if 

 that portion of the shell be taken alone the spiral angle of the 

 whole may be represented as greater than it really is. There are 

 tv7o unnamed shells in the Brussels Museum from Vise which are 

 identical with the British specimens, and the clearly-preserved lines 

 of growth show the sinus to be in the same position. The M. quaclri- 

 carinata of De Koninck appears to me to be a small variety of this 

 species. M. conula, var. convexa, may be distinguished from 

 31. quadricarinata, M'Coy, by its more prominent sutures, less 

 angular whorls, fewer and differently disposed keels, and by its 

 flattened base. It is like it, however, in having the sinus above 

 the angle. 



Locality and Formation. The variation in size of different indi- 

 viduals is somewhat remarkable. The largest English shell (PI. XVI. 

 figs. 8, 9) is from shales at the base of the Yoredales at Abbey 

 Foss, Askrigg, Yorkshire. It consists of eleven whorls ; the apex is 

 broken, so there would probably be four or five more if entire. It 

 is 34 millim. in length ; the w^idth of the body-whorl is 12| millim. 

 None of the Scottish specimens equal this in dimensions. The largest 

 that I have seen is in the collection of Mr. John Young, Hunterian 

 Museum, Glasgow, from the shales of the Lower Limestone Series 

 of Craigenglen, Campsie. It consists of twelve whorls; the apex is 

 broken, but if the specimen were entire there would probably be 

 two or three whorls more. The length is 16^ millim. ; width of 

 bofly-whorl 5 millim. ; height 4 millim. The larger of the two 

 Belgian specimens referred to is from Vise, etage v 2 ; it is embedded 

 in the matrix, and only shows nine whorls, which have a length of 

 3 7 millim. De Koninck gives 45 millim. as the length of the type. 

 Other specimens from various localities in Yorkshire, Scotland, and 

 Belgium vary in size from these dimensions down to shells which 

 have as many as eleven or twelve whorls in a total length of 6 millim. 

 Small, well-preserved external casts of this species are found in an 

 impure limestone of Yoredale age at Mosedale, on the northern 

 slopes of Widdle Fell. 



