36 FOSSIL MEDUS 2. 
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. 
Hic. 11.—Laotira cambria. Hypothetical canal system of the exumbrella of fig. 1 of Pl. 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 was the oral arms 
turned upward and interlocked with the exumbrella lobes, in the extreme 
