248 SIDNEY F. HAUMER. 



accordingly connected witli the opening of the tube by a pair 

 of nearly vertical flanges, which are situated in a transverse 

 plane; thus forming a smooth surface over which the tentacle- 

 sheath can glide easily in its movements of eversion and 

 retraction. In the type-specimen (a) the distal margin of 

 the tube is produced into two strong horns, which curve 

 downwards towards the basal surface. It is probable that 

 these serve as the point of origin of muscles or ligaments 

 which regulate the movements of the tentacle- sheath. 



In some cases (particularly in specimen d) the origin of the 

 tube from the cryptocyst is almost as asymmetrical as in 

 S. lateralis, though without the deep sinus of the latter. 

 Tin's condition is not so easily observed in other cases. 



In the specimens (/) and (d) tliere are some interesting 

 variations in the median process. In some zooecia this struc- 

 ture has the typical form (as in fig. 2), being broad and markedly 

 silicate. At the opposite extreme the process is T-shaped 

 (fig. 29) as seen from above, with nearly transverse distal 

 border, ending in a sharp point on each side, a linear lon- 

 gitudinal portion connecting the distal border with the 

 descending cryptocyst. Even in extreme cases the linear 

 portion slightly widens proximally, and an indication of the 

 longitudinal groove can usually be made out here. All 

 stages exist between this condition and the typicnl sulcate 

 form. 



The edge in this species is but slightly raised. The post- 

 oral shelf is narrow, especially proximally, and is sharply 

 separated from the cryptocyst ; it is continuous with a thick- 

 ened tubercular portion which runs along the angulated part 

 of the cryptocyst. The transverse thickening is not quite 

 complete medianly in the single B zooecium (fig. 2) which has 

 been examined. This differs from the a zooecia in the 

 greater size of the distal or subopercular cavity. The oral 

 shelf is quite absent. The condyles for the origin of the 

 hinge of the operculum are conspicuously long, and at right 

 angles to the lateral walls of the zooecium. The oral arch is 

 ^ moderately raised above the level of the epitheca. The 



