SOUTHAMPTON ISLAND, HUDSON BAY.
Streptelasma robustum, Whiteaves.
This large and well marked species, described originally from the Galena-Trenton of the Lake Winnipeg region, is represented by a number of more or less fragmentary specimens. The inner structure is well shown in transverse and longitudinal sections.
Favosites gothlandica, Lamarck.
Over forty specimens from this locality are referable to this well known species. In many of them are seen the spiniform septa, characteristic of all Silurian favosites, and distinguishing them from all Devonian forms which apparently without exception possess linguiform septa. It is possible that more than one species may be here represented. The range in size of the corallites in F. gothlandica has been noticed by the writer in his ‘Revision of the genera and species of Canadian Palæozoic corals[*],’ 1899-1900, but in the present collection the fragmentary condition of most of the specimens does not admit of characters dependent on the outward form of the corallum being used with any degree of certainty.
| [*] | In this report the reader will find extended references to the structure of the majority of the species mentioned in these notes. |
Syringopora verticillata, Goldfuss.
A single specimen of this species was obtained at Southampton island. Its corallites average about 4 mm. in diameter and are rather lax and irregular in their growth, the result of which is that the connecting tubes are poorly developed and comparatively distant. This particular mode of growth is admirably shown in specimens, in the possession of the Survey, from the north end of Lake Timiskaming.
Halysites catenularia, L.
Represented by a small corallum, round which has grown a stromatopora. This coral exhibits the structure characteristic of the typical form of the Niagara formation, viz., moderate sized corallites, oval in transverse section with narrow tubules intervening. Four corallites are included in a space of 8 mm.
This form also occurs in the Guelph limestone of Ontario.
A second and particularly interesting specimen was obtained by Mr. Low at Southampton island. It differs from the typical form in having corallites of noticeably large size, and agrees in this particular with a specimen from the Guelph limestone at Durham, Ont. (J. Townsend, 1884), in the museum of the Survey. The Durham fossil has not the finer details of structure sufficiently well preserved to show the minute tabulæ of the tubules, but in Mr. Low’s specimen longitudinal sections of the tubules clearly reveal the highly arched, close set tabulæ within. There are three corallites in a space of 12 mm., as in the Durham specimen, and the tubules have a width of about ·75 mm.
Plasmopora follis, M.-E. and H.
To this species is referred a small specimen showing the inner structure fairly well. The corallites vary in diameter from slightly under to a little over 1 mm., and they are mostly less than their own diameter apart with from one to three tubules, in the shortest line, between neighbouring corallites. This species is generally considered to be typical of the Niagara group.
Pycnostylus elegans, Whiteaves.
A few specimens weathered so as to show only the inside of the corallites which vary in diameter from 7 to 15 mm. An interesting feature of these specimens is the preservation of the free edges of the septa which are seen to be denticulated, about seven denticles occurring in a space of 2 mm. A re-examination of the type material reveals the presence of these denticles, although they are poorly preserved. Mr. Low’s specimens are referable to the species from the Guelph limestone of Ontario with large corallites (from 13 to 17 mm. in diameter) as in the other and type species from the same horizon and district, the corallites are generally smaller (from 3 to 7 mm. in diameter). As suggested by Dr. Whiteaves in his original description, additional material with corallites of intermediate size may prove the two forms to be specifically identical.
Of the corals from Southampton island, Streptelasma robustum indicates the presence of beds at this locality that belong to the same horizon as those that have been assigned to the Galena-Trenton in the Lake Winnipeg region, and similar beds exposed over a large area to the west of Hudson bay. The beds from which the other species from the same island are derived belong to higher horizons which are, on the evidence of these species, of about the same geological age as those of the Niagara and Guelph formations of Ontario.