By] FOSSIL MEDUS2&. 
LAOTIRA CAMBRIA Walcott. 
Pls. VN-XIX, XXI-XXIII. 
Laotira cambria Walcott, 1896. Proc. U. S. Nat. Mus., Vol. X VIII (1895), p. 613, 
Pl. XXXU, figs. 1-8. 
The description of this species will follow in arrangement that of 
Brooksella alternata. Its variations, however, are greater, and the descrip- 
tions will be divided into, first, the simple forms, and second, the compound 
forms. Individuals vary in size from 1.5% to 8° in diameter, the average 
size of the simple forms being about 5°. 
Umbretla— The general form of the simple type is subspherical to de- 
pressed-convex, and that of the compound type varies from nearly circular, 
semiglobular forms to irregularly transverse, flattened disks. The simple 
type is illustrated by figs. 1, 4, 7, 10, and 11 of Pl. V, and the compound 
type by fig. 6 of Pl. VIII, 7 and 7a of Pl. LX, 6 and 6a of Pl. X, and 3 of 
Pl. XI. The lobation of the exumbrella varies from the simple four-lobed 
variety (PI. V, figs. 1, 4, and 10), through the series represented by figs. 7, 9, 
and 11 of PE V1, )2),40 5a, 7, and 8yok Pl Vile 2 and 4sor Ele Villie2onslals 
VIII; 3, 4, 6, and 7 of Pl. IX, and 2 and 3 of Pl. XI, to the compound type 
shown in Pl. XII, figs. 1,2, and 3. The variation in form and arrangement 
of the lobes is also shown by the same series of figures. As in the case of 
Brooksella alternata, the form varies with the condition of preservation. In 
figs. 5 and 10 of Pl. V the original form is obscured by a deposition of sili- 
ceous matter over the original body of the medusa. This is not a rare occur- 
rence, as about 10 per cent. of the specimens exhibit more or less of it. In 
a large number of individuals the firm ectoderm preserved the original out- 
lines, and, with the exception of the flattening as the result of collapse after 
death, the original plumpness and rotundity of the lobes are preserved. 
The subumbrella varies more than the exumbrella. Figs. 1 and 11a of 
Pl. V, la and 2a of Pl. VI, and 1a and 7 of Pl. VIL, illustrate the regular, 
simple type; but in fig. 1 of Pl. X the almost simple type of the exum- 
brella, like fig. 1 of Pl. V, has a complex subumbrella. The same is also 
well shown by figs. 1 and la of Pl. XI. The progressive variation of the 
complexity of the subumbrella is exhibited by fig. 1 of Pl. V, la of Pl. VII; 
3a, 5a, 6a, and 7a of Pl. IX; 4, 6, and 7 of Pl. X; 1a and 2a of Pl. XI, and 
2a of Pl. XII. The series of figures illustrate the variations much better 
than they can be described in detail; but attention will be called to a few 
