Ru EDEM A NN— S ESSILE C( ) N U L A U I A . 



713 



The distal margin of the shells is composed of small denticles which 

 develop into the apertural processes of the adult stage. In all the broader 

 specimens there terminate, between these denticles, longitudinal lines, which 

 are of darker color than the other film and which divide the latter in sections 

 of equal size (cf. tigs. 5, 7, 10, PI. IV). They are, as shown by their position, 

 the first indications of the marginal grooves observable in this early stage. 

 The appearance of several of these denticles and grooves on the broader speci- 

 mens indicates that the apparent great breadth of the youngest stage is 

 largely due to a complete flattening. This explains also why a few specimens 

 have been found the marginal angle of which is not much larger than 

 that of adult forms (cf. figs. 8 and 9). 



Such abruptly broadened shells as that reproduced in figure <> are a 

 common occurrence. It is obvious that in this case the shell burst at this 

 point and became subsequently more distally unfolded. 



Even larger shells, though by far not so common as those of the smallest 

 stage, were subjected t<> bursting and spreading in one plane. Figures 17, 18, 

 25, 28 and 31, Plate IV, are taken from such specimens. The crushing 

 sometimes led even to a separation of the faces, as in the original of figure 

 11. The infrequent observation of adult specimens of Cormlarki which are 

 complete, in comparison to the profuse occurrence of fragments of faces, 

 may be largely due to such separation of the faces before becoming covered 

 by sediment. 



A remarkable feature of many of these minute shells is the darker 

 appearance of the basal appendage when compared with the living chamber. 

 Shells where this difference is especially noticeable are reproduced in figures 

 5 and 7. This difference can, no doubt, be accounted for by the different 

 thicknesses of the chitinous walls, and this is also indicated by the less com- 

 pressed condition of the basal appendages in more advanced stages (cf. PI. 

 IV, figs. 12, 13, 14, 18, -2-2, and especially PI. I, tigs. 2 and 5; PI. II. tig. 1 ). 



Increasing in length, the shell generally becomes more slender in shape 

 (cf. PI. IV, tius. 1.°) to 82), though specimens with oval outlines are by no 

 means rare (cf. tigs. 17, 21, 29). In looking over the slalis with the naked eye, 

 it will even seem as if all the tiny fossils consisted of carbonaceous oval bodies 

 with a disc or ring at one end. The glass, however, will in the majority of 

 the specimens reveal straight margins (cf. tig. 26) and a truncated (cf. fig. 

 21) or acute (cf. fig. 30) distal end. 



The relatively large size of the basal appendage in the smallest forms has 

 already been mentioned. Though in these smallest specimens the details of 



