38 FOSSIL MEDUS&. 
more finely exhibited by fig. 6 of Pl. XIII, and the more flattened individual 
represented by fig. 5 of Pl. XII. The lower surface of fig. 1 of Pl. XII 
is, unfortunately, not sufficiently well preserved to be illustrated. It was a 
combination of the characters seen in figs. 5 and 6a of Pl. XII Fig. 1 of 
Pl. XXI is a portion of the lower surface of a large complex individual 
of the type represented by fig. 6 of Pl. XII. The variety of form of the 
complex type is almost endless. This is owing to the original variation 
and to the incidents of the embedding and preservation of organic remains 
so liable to be distorted by pressure and their own weight. 
The presence of axial oral arms, such as occur in Brooksella alternata, 
is of rare occurrence in Laotira cambria. It is fairly well shown in figs. 3 
and 3a of Pl. VIII, where several arms project out between the exum- 
brella and subumbrella. 
Oral plate—The oral plate may be formed in the simple types by the 
union of the oral arms at the center (as in Brooksella), but in the complex 
forms no true plate can be said to exist. 
Cireulation—The circulation of the complex forms may have been by the 
intaking of food through the oral pores or tubes of the various irregular, 
individual, or combined oral lobes of the lower surface of the organism, 
followed by its passage through the irregular interior canals and_ final 
expulsion through the exterior openings of the exumbrella canals. Such 
would be anticipated to be the case if we should begin with the simple, 
regular forms, and trace the structure as it gradually becomes more and 
more complicated. 
Reproduction—No traces of the reproductive system have been observed 
in Brooksella, and none in Laotira except what appears to be a process of 
fission. No true sexual organs have been recognized. Reproduction by 
fission is indicated by the specimens represented on Pl. XIX, figs. 2 and 
3. In these, two otherwise entire, simple individuals are held together by a 
single lobe, the severing of which would set them free. Fig. 1 of that plate 
illustrates a more complete union of two, and fig. 1 of Pl. XIII of three or 
more. In fig. 6 of Pl. XII there is a general appearance of looseness that 
might give rise to the view that a portion would have soon separated as a 
distinct individual. The same is also true of the double form, shown by 
fie. 3 0f. Pl) XII. 
Reproduction by lateral fission is of rare occurrence among the recent 
medusze. Kolliker describes an instance among the Discomedusee—in the 
