44 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE. [VOL. XI 
are about .5 to I mm. apart. On the concave side of the corallum they 
turn upwards in a sigmoidal curve, at first convex upwardly and later 
concave. These elements seem to form a central spongy zone with the 
inner edges of the septa. On the convex side of the corallum the course 
of the dissepiments is shorter, but owing to mineralisation the structure 
is not well revealed. 
The form is evidently a large species of Streptelasma, but its specific 
determination is impossible on account of the fragmentary nature of 
the specimen: it much resembles the figure given by Whiteaves for 
S. robustum on Plate XVII, Vol. III, Palaeozoic Fossils, but the absence 
of secondary septa makes the transverse section very different from 
that figured by Lambe for S. robustum on Plate VII, Vol. IV, Cont. 
to Can. Pal. 
Streptelasma robustum is an Ordovician species, whereas the associ- 
ations of the present example are Silurian. It is unlikely that we are 
dealing with a strictly co-specific type, but the condition of the specimen 
does not justify more than a comparison. 
Locality—Above Limestone rapids, Severn river, District of Patricia, Ontario. 
Horizon—Silurian. 
No. 289 S. Royal Ontario Museum of Palaeontology. 
Cf. ZAPHRENTIS STOKESI, Milne-Edwards and Haime. 
ZAPHRENTIS STOKESI, Milne-Edwards and Haime. Polyp. Foss. des Terr. Palaeoz., p. 330, 
pl. 3, fig. 9, 1851. 
?CANINIA BILATERALIS, Hall. Pal. N.Y., Vol. II, p. 41, pl. 17, fig. 3, and p. 113, pl. 32, 
fig. 3, 1852. 
?POLYDILASMA TURBINATUM, Hail. Ibid. p. 112, pl. 32, fig. 2, 1852. 
ZAPHRENTIS STOKESI, Billings. Cat. Sil. Foss. Anticosti, p. 34, 1866. 
ZAPHRENTIS STOKES!, Nicholson. Pal. of Ont., pp. 43 and 58, 1875. 
ZAPHRENTIS STOKESI, Rominger. Geol. Sur. Mich., Foss. Corals, p. 144, pl. LI, three 
figures in lower row, 1876. 
ZAPHRENTIS STOKESI, Lambe. Geol. Sur. Can., Cont. Can. Pal., Vol. IV, pt. 21, p. 120, 
pl. IX, figs. I, 1a and 2, 1900. 
It is with considerable doubt that the specimens in hand are referred 
to this species: some of them are badly broken, while others, apparently 
in good condition, are so filled with secondary thickenings that the 
nature of the internal structures is not clearly revealed. 
All the specimens show an intermediate stage between the typical 
structure of Streptelasma and that of Zaphrentis. The central reticulate 
area of Streptelasma is not seen, but on the other hand the continuous 
tabule of Zaphrentis are but ill defined. 
One small and fairly well preserved specimen presents the follow- 
ing features: Corallum turbinate, 35 mm. long in a straight line; maxi- 
