29 



ribs. As vieweil along tlie siphonal edge, the whole of the eostation is 

 rather fine in proportion to the size of the shell ; near the aperture, the 

 greatest distance between the summits of two contiguous ribs (on the per- 

 iphery) rarely amounts to as much as two lines, the average being about 

 a line and a-quarter. 



The specimen figured, which although in some respects the most per- 

 feet of the two, is very much distorted, measures about five inches in its 

 greatest diameter, the width of its umbilicus being about eighteen lines. 

 The other is four inches and two lines across, and its umbilical cavity is 

 fifteen lines wide. 



A. LoGANiANUS (?) Form A. 

 Plate IV., figs. 2, 2a. 



Shell subglobose ; inner whorls entii-ely covejcd except the outer half 

 of the last one; umbilicus rather small. 



Outer whorl somewhat inflated, broadly rounded on the peripher}-, and 

 sKghtly compressed at the sitles. Umbilical cavity rather more than 

 one-lourth oi' the entire diameter, deep in the centre and shallow ex- 

 teriorl}". Margin of the umbilicus rounded, its inner fiice steep but 

 low. Behind the mouth of the shell there is a broad and moderately 

 deep groove or constriction, and the whorl contracts very perceptibly at 

 a short distance from the apertui-e. Near the sutures there is a shallow 

 sinus on each side of the lip, which is produced into a broadly rounded 

 process on the periphery. The groove behind the mouth seems to follow 

 the contour of the outer lip, unless the latter once bore lateral lobes, of 

 which there is no, evidence. The aperture is transversely arcuate, its 

 breadth being neai'ly three times as great as its height. Tn the middle 

 of the same whorl, before it begins to narrow, the height of the volution 

 is much greater in pi-oportion to the width. 



The sculpture consists for the most part of primary ribs, which rise 

 from the sutm-es, and bifurcate at about a third of the distance across 

 the sides, hnfore passing over the periphery. About eighteen of these can 

 be counted on the outer whorl. The points of bifurcation are not marked 

 by any distinct swellings or tubercles. Occasionally a simple and shorter 

 rib intervenes between a pair of primaries, but the intermediate ribs are 

 often wanting altogether, and when present never reach to the sutures. 

 At fii'st the eostation is comparatively close set and the ribs, with their 

 corresponding grooves, ai-e subangular, but in the last half turn they get 

 wider apart and more rounded. The whole sculpture is very coarse 



