406 



DR F. A. BATHER. 



The stem may be divided into three parts : a proximal region, of four pairs of 

 ossicles ; a middle region, of one large conical columnal ; and a distal region, of narrow 

 circular columnals. 



§ 201. The ossicles of the Proximal region {text-figs. 19-23) may be regarded most 

 simply as four rings, each split in two by a vertical suture corresponding with the 

 suture at the thecal base. The lumen of this region was wide, and so far as can be 

 made out (see especially GrIO, PI. III. fig. 36 ; also G26) the thin and possibly folded 

 edges of marginals 4 and 5 dipped into it. These half rings or dimeres often alternate 

 at their edges (text-figs. 19, 21), but this arrangement may be due to post-mortem 

 shifting. The same cause may have given rise to an observed imbrication, now in a 



Fio 19. 



Fm. 20. 



Fig. 21 



Fig. 23. 



Text-figs. 19-23.— CothurnocysUs Elizae. Sketches of the proximal and median region of the 

 Stem, enlarged about 2 diameters. 



Fig. 19. — From G45, obverse view. Note the granular ornament. 



Fig. 20. — From G6, reverse view. Note the fused dimeres of the fourth pair (cf. PI. III. 



fig. 28). 



Fig. 21. — From G 25, reverse view. Note the irregularity and ])artial alternation of the dimeres. 



Fig. 22. — From G 59, reverse view. The dimeres are shifted, and expose a grooved under surface. 



Fig. 23.— From G 42, reverse view. The dimeres are much disturbed and their grooved structure 



plainly indicated. 



distal, now in a proximal direction (text-fig. 22) ; but often the rings abut regularly, 

 and this seems to be the more normal arrangement. The actual structure seems to be 

 that the lower joint-face of each dimere is grooved to receive the upper joint-face of 

 the dimere above, but sometimes the outer margin of the groove may be the more 

 developed, as in G6, G31, and G34, in which case there is a tendency to distal 

 imbrication ; or sometimes the inner margin may be the more developed, in which case 

 the imbrication appears proximal, as in G42 and G59. The dimeres of the distal ring 

 tend to be more firmly joined to each other than do those of the other rings {e.g. G6, 

 G25, text-figs. 20, 21). In all points, then, the structure of the proximal region is 

 variable, and has not attained the definite and pronounced character seen in C. curvata 

 (§ 220). 



