139 



individuals appear between the larger eorallites of the mon- 

 ticules, occasionally between those of the interspaces. Cor- 

 allites with fine transverse strife; walls of uniform thickness 

 throughout; tabula? at irregular intervals, remote in older 

 parts of tube, more closely set in outer portions. 



This coral is almost always found encrusting Aulopora 

 tubceformis, which in turn grows on shells of Spirifer gran- 

 ulosus. These shells when full-grown apparently became 

 free, and rolling over, so as to lie on the pedicle valve, allowed 

 the growth of the Aulopora on the upturned brachial valve 

 — particularly on the mesial fold. No shell with the coral on 

 the pedicle valve has been observed. All the specimens 

 obtained showed the Monotrypa growing on the Aulopora 

 in various stages of development. The specimen (Fig. 22a) 

 shows the most advanced stage, where the Monotrypa has 

 completely enveloped the Aulopora, as well as the greater 

 portion of the shell. It has forced the Aulopora to depart 

 from its normal method of growth (compare Fig. 16), which 

 is prostrate, and bend upward, at right angles, its calices 

 appearing on the surface, like a series of crater-like rims, 

 rising above the monticules of the Monotrypa. The two 

 types probably lived together as commensals, judging from 

 the constant association, although in places the Aulopora 

 becomes completely overgrown by the Monotrypa. This 

 may indicate a choking of the former b}' the latter, or it may 

 mean burial after death. In several parts of the specimen 

 (Fig. 22a) the encrusting corals near the front have grown 

 beyond the edge of the shell, and there assumed the cylin- 

 drical outline of the colony, similar to that of M. fruticosa. 



Found in the middle and upper Pleurodictyum beds of 

 Averv's Creek and Wanakah Cliff; also in the Calcareous 

 bed, above the Pleurodictyum bed, at Avery's Creek. 



Class Crinoidea. Miller. 



The crinoids, or sea-lilies, are marine invertebrates, represented in the 

 modern seas by a number of genera and species, winch range from shal- 

 low water to a maximum depth of about 3,000 fathoms. They are 

 gregarious in habit, and usually of very local distribution. A typical 



