32 FOSSIL MEDUS/E. 



LiAOTIRA CAMBRIA Walcott. 



Pis. V-XIX, XXI-XXIII. 



Laotira cambria Walcott, 3896. Proc. TJ. S. Nat. Mus., Vol. XVIII (1895), p. 613, 

 PI. XXXII, figs. 1-8. 



The description of this species will follow in arrangement that of 

 BrooJcsella 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 cm to 8 cm in diameter, the average 

 size of the simple forms being about 5 cm . 



umbreiia. — 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 PI. V, and the compound 

 type by fig. 6 of PI. VIII, 7 and 7a of PI. IX, 6 and 6a of PI. X, and 3 of 

 PI. XL The lobation of the exumbrella varies from the simple four-lobed 

 variety (PL V, figs. 1, 4, and 10), through the series represented by figs. 7, 9, 

 and 11 of PI. V; 1, 2, 4, 5a, 7, and 8 of PI. VI; 2 and 4 of PI. VII; 2 of PL 

 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 la and 7 of PL VII, 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 XL 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; la 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 



