36 



FOSSIL MEDUSAE. 



of a complex type which have been studied, or to the nonpreservation of the 

 interior canals in the fossil state. 



oral opening and arms. — No central oral opening has been seen. It is highly 

 probable that one did exist in the simple, regular forms of the young, but 

 not even a trace has been seen of a depression at the base of the central 

 axis; usually there is no trace of mouth, regular oral arms, or oral plate. 



Fiq. 11. — Laotira cambria. Hypothetical canal system of the exumbrella of fig. 1 of PI. XIV. The canals are 

 drawn in from other specimens in which they are exposed by weathering. 



There is, however, a group of specimens that present characters indicating an 

 unusual development of the oral arms in the simple type. My first impres- 

 sion was that two individuals were pressed together at their ventral surface, 

 but as more and better specimens were collected, this finally gave way to the 

 view that what had been considered as a second individual Avas the oral arms 

 turned upward and interlocked with the exumbrella lobes, in the extreme 



