﻿555 



PL xii, and in Fig. i, PI. xiii, which is the reverse of that of Fig. 

 30, but enlarged two diameters. The presence of an annular lobe 

 is noted as it appeared in the specimen, but this part was covered 

 by remnants of the nacreous layer and it was not positively denned. 

 The dorsal furrow began between the first and second septum and 

 is faintly shaded in Fig. 1, PL xiii. The dorsal sutures were cov- 

 ered except as far as represented. The side view, PL xiii, Fig. 2, 

 shows these sutures, so far as seen, the last two in this figure being 

 the first two of Fig. 29, PL xii. 



The broad costae of the genus made their appearance in the ana- 

 neanic substage at the same time that the septa approximate and 

 the zone of contact is formed. 



It will be observed that the costse are broader at first than they 

 are in later age even in this figure, showing that growth was more 

 rapid at first as in the development of the septa. 



Eutrephoceras* n. g. 



This genus includes these forms like the type Eulrephoceras 

 Dekayi, which have globose ananepionic substages, increasing subse- 

 quently with great rapidity in all their diameters. The ana- and 

 metanepionic substages are highly tachygenic and these shells have 

 very small, and often hardly perceptible and much flattened, um- 

 bilical perforations. The siphuncles are subdorsal! from the apex 

 through the nepionic stage in some species, in others this position 

 is not maintained, but the siphuncle is generally in later stages 

 near the dorsum and in the ephebic stages it is dorsad of the 

 centre. 



The nepionic stage has longitudinal ridges and transverse bands, 

 the former disappearing in adults which are smooth. 



The form of the whorl in section is nephritic from an early age 

 and changes but little throughout life. 



The sutures are almost straight, having but slight ventral lobes, 

 broad ventrolateral saddles, lobes on the umbilical zones and deep 

 lobes in the zone of impression. There are no annular lobes at 

 any stage of development. 



* Eurpecprjq, clasping around. 



