44 FOSSIL MEDUSA. 



Before any direct comparisons between D. asteroides and Laotira Cam- 

 bria are made, attention is called to the fact that nearly all the specimens of 

 the former species are crushed flat in the slate and that those of L. cambria 

 are usually convex. A few specimens are flattened on the chert nodules and 

 afford the means of comparison of specimens preserved under nearly the 

 same conditions with reference to their compression and distortion. 



Fig-, e of PI. XXVI has seven lobes, one of which is pressed out 

 broadly at the outer end. Fig. 5 of PL XXII has six lobes, one of which 

 is similarly expanded. The general appearance of the two specimens is 

 similar. In Fig. 6 of PL XXII the lobes, where not broken off, are flat- 

 tened and pressed out at the outer portion, somewhat as in tig. h of PL 

 XXVI. The lobes of fig. 6 of PL VI are more convex than those of fig. d 

 of PL XXVI, but the general form is the same. Of the four-lobed speci- 

 mens, fig. 1 of PL XXV may be compared with fig. 10 of PL V, and of the 

 five-lobed, fig. 2 of PL XXIV with fig. 2 of PL XXI. Of the specimens 

 indicating reproduction by fission, compare fig. 2 of PL XXV with fig. 2 of 

 PL XIX. When comparison is made between some of the examples of the 

 two species they appear to be generically identical, but a series of speci- 

 mens shows a looseness of structure in D. asteroides (as in fig. 1 of PL XXIV, 

 fig. 3 of PL XXV, fig. c of PL XXVI) that is not met with in L. cambria or 

 B. alternata. The range of variation in the number of lobes is also much 

 less — 4 to 7. 



Our knowledge of the details of this genus and species is too limited 

 for a clear generic and specific description. Of the genus it may be said 

 that it is a discomedusan with a lobate umbrella, 4 to 7 or more lobes; 

 without tentacles and without (?) central oral opening in the adult; with a 

 central radial canal in each lobe, which enters a central stomach. This 

 applies to such forms as those illustrated by fig. 2 of PL XXIV, fig. 1 of 

 PL XXV, and figs. 6, d, and e of PL XXVI. There are other forms (fig. 1 

 of PL XXIV, fig. 3 of PL XXV, figs, c and e of PL XXVI, etc.) that pre- 

 serve more or less of the subumbrella surface, and from them we learn that 

 the subumbrella lobes were narrow and united at the center, as in many 

 examples of Laotira cambria (figs, la and 2a of PL VII, fig. 3a of PL IX). 

 It is to be remembered that the Lower Cambrian specimens are compressed 

 and flattened between the laminae of the slate. With this in mind we can 

 understand how the forms illustrated by fig. 3 of PL XXV and fig. 6 of PL 



