166 GENESIS OF THE ARIETID.E. 



Var. C. 



The adults are remarkable for, their prominent straight keels. The channels 

 when present are very shallow. The young remain smooth for a longer time 

 than in other varieties. The pilse appear between the first quarter of the fourth 

 and first quarter of the fifth whorl. 



While smooth throughout the first three or four whorls, it is identical with 

 the adults of miserabile, var. acididorsale, but the sutures are more immature. The 

 pila? develop quickly, and are similar to those of variety B. In fact, the young 

 can be distinguished only by the larger size, quicker growth, and smaller num- 

 ber of the pilse. Associated with these are specimens with compressed whorls, 

 perhaps males. 



Var D. 



Plate II. Fig. 15, 15 a. 



This has a narrow abdomen, and the pilse are more prominent near the dor- 

 sum. They appear on the fourth quarter of the third, or on the first half of the 

 fourth whorl, earlier than in some specimens of variety B, and are more slowly 

 developed. Some of the young are very like the adult of Am. miserabile, var. 

 cuneiforme. The pilse bend forward when they first appeal-, or soon after, as in 

 this variety, although subsequently becoming straight, like those of the adults of 

 variety A. The abdomen is sharp, as in miserabile, var. acididorsale ; the keel does 

 not appear until the pilse begin to acquire their prominent, straight adult char- 

 acteristics. The sutures have serrated outlines. 



The abdominal lobe (Plate II. Fig. 15 a) ma}' be equal to the superior lateral 

 lobes, or one fourth shorter, and the siphonal saddle is remarkably large. The 

 superior lateral saddles are divided symmetrically, and are equal in depth to the 

 inferior laterals. The superior lateral lobes are very broad, and about one half 

 longer than the inferior laterals. These characteristics were observed on the 

 third quarter of the fifth volution of a specimen from Semur. In specimens from 

 Whitby, on the second quarter of the same volution the sutures are similar in all 

 respects, but the superior lateral lobes are at first equal to the abdominal lobe 

 in successive sutures, and then slightly longer. At still earlier stages, when the 

 marginal lobes first appear, the abdominal lobe is usually of the same depth as 

 the superior laterals, or shallower (Plate II. Fig. 15 a). One specimen from Semur 

 had sutures maintaining these immature proportions even on the latter part of 

 the fifth whorl. 



There are several specimens from Spezia in Bronn's collection, Museum of 

 Comparative Zoology, labelled by Capelini Amm. subarietinus, Menegh. These seem 

 to belong to this species, but are so compressed that it is difficult to make sure of 

 the identification. The young are smooth until a very late stage, as is usual in 

 semicosiaium, and the pilse and form are also similar. They are in the yellow 

 clayey shale, and described as from Coregna near Spezia. 



