g4 The Canadian Field-Naturalist [Vol. XXXVI 



THE DISTRIBUTION OF THE OTTAWA TRENTON ECHINODERM FAUNAS 



By a. F. Foerste 



THE Trenton limestone of the Ottawa area is 

 characterized by an interesting fauna, part 

 of which is very restricted in its geographical 

 distribution. This is true especially of its echino- 

 derms, including the cystids, crinoids, and star- 

 fish, which are represented by a considerable 

 variety of species, some of which are fairly common. 

 The same species as those found at Ottawa, or 

 closely related forms, occur also 170 miles south 

 west of Ottawa, at Kirkfield, on the Trent canal,, 

 between Simcoe and Balsam Lakes. These two 

 localities, Ottawa and Kirkfield, are widely 

 known for the richness of their Trenton echinoderm 

 faunas. A small exposure on Goat Island, north- 

 east of Little Current, on Manitoulin Island, 300 

 miles almost directly west of Ottawa, has fur- 

 nished a small echinoderm fauna of such variety 

 that it is probable that if considerable exposures 

 were at hand, the number of species here also 

 would be considerable. This Goat Island fauna 

 evidently is closely related to that found in the 

 Trenton at Ottawa. Farther westward the 

 Trenton echinoderm fauna of the Ottawa area is 

 represented only by occasional species. 



Six hundred miles west of Ottawa, on the 

 Escanaba River, northwest of Green Bay, an 

 arm of Lake Michigan, in section 17 of township 

 41 of range 23, the very characteristic Ottawa 

 species, Comarocysiites punctafus Billings, occurs 

 associated with the widely distributed species 

 Pasceolus globosus Billings, and with the New 

 York Trenton species, Schizocrinus nodosus Hall. 

 About 10 or 20 feet farther up, another New 

 York Trenton species, Cheirocrinus anatiformis 

 (Hall), is found. These species were collected 

 long ago by Dr. Carl Rominger, at that time 

 State Geologist of Michigan (Geological Survey 

 of Michigan, Vol. I, 1873, pp. 58-60). Recently 

 the writer had an opportunity of examining the 

 original specimens of Comarocysiites and Pasceolus 

 collected by Rominger, and now deposited in the 

 Geological Museum belonging to the University of 

 Michigan. The Comarocysiites specimen, num- 

 bered 5405, evidently is a typical representative 

 of the species C. punclatus, as recognized already 

 by Rominger. 



The specimen of Pasceolus, numbered 5403, 

 however, was described by Rominger in the 

 following paragraph which leaves its identity 

 unestablished: 



"Bryozoa. Chsetetes petropolitanus, Chsttetes 



ramosus, and several other forms, of which one 



is interesting enough to be described here. It is 

 of small mummiform shape, with conspicuous 

 solid dots, formed by closed tubes and closed 

 finer interstitial cells. These solid dots in 

 some specimens project like warts, and are 

 surrounded by a depressed polygonal area, 

 which gives the surface a striking similarity 

 with a compound star-coral. Perfectly iden- 

 tical specimens also occur in the Trenton 

 limestone of Canada, near Ottawa river, and 

 are preserved in the collections of the Geological 

 Survey at Montreal." 



The preceding description becomes readily 

 intelligible, when compared with the specimen 

 belonging at present to the University of Michi- 

 gan. The latter is depressed globose in form, 38 

 mm. in diameter, and 22 mm. in height. It is 

 covered with numerous hexagonal and pentagonal 

 plates averaging from 3 to 3.5 mm. in diameter. 

 The sutures between these plates are clearly 

 defined. The central part of the plates is de- 

 pressed, and from this depressed area grooves 

 radiate outward in a stellate manner toward 

 the angles of the plates, usually disappearing 

 before reaching the latter. It is these stellate 

 grooves which suggested to Rominger a striking 

 similarity with a compound star-coral. All 

 specimens of Pasceolus globosus do not show these 

 stellate grooves. In some specimens the plates 

 present moderately convex surfaces, suggesting 

 to Rominger solid dots, projecting like warts. 

 The appearance of warts projecting from the 

 general mass is due to weathering, which has left 

 narrow grooves between some of the plates. 

 There are no interstitial cells; Rominger was 

 deceived by irregularities along some of the sutures. 

 A break across one of the plates, parallel to its 

 surface, shows that what appear as sutures at the 

 surface are in reality vertical walls, very thin, 

 which can be traced for a distance of 1 mm. 

 beneath the surface, but no other structure can 

 be observed in the interior of the Escanaba speci- 

 men. 



At present there is a tendency to regard Pas- 

 ceolus as one of the calcareous algse in which a 

 central space is surrounded by a single spherical 

 layer of cells completely shutting off the interior 

 cavity. The cells present polygonal outlines due 

 to lateral pressure. The walls separating the 

 cells are very thin. The outer walls, facing the 

 exterior, are either concave and with stellate 

 grooves, or convex and without any other con- 



