ACTrXOCEEATID^. 
199 
so as to increase the diameter. The siphuncle is very large in pro- 
portion to the size of the shell ; the segments of which it is com- 
posed are slightly oblique to the axis, and their surfaces flattened 
along the inner curvature of the shell, as in D. remoUis. The 
inner layer of the test must have been extremely thin, as the septa 
show very distinctly through it. A fragment of the outer layer is 
preserved, and this presents a perfectly smooth surface. 
The endosiphon is seen somewhat obscurely in one of the spe- 
cimens (fig. 26 B). Judging by the appearance of the sheath in the 
same example, it is probable that we have here the whole of the 
septate part of the shell. 
Remarls. JJiscosorus gracilis is readily distinguished from D. 
conoideus and D. remotus by its more slender proportions and some- 
what slower rate of tapering. 
Horizon. Niagara Group (Wenlock). 
Localities. Drummond Island, Lake Huron ; Niagara. 
Fairly well represented in the Collection. 
, Genus HURONIA, Stokes k 
{Orthocbres Longicones — Group 18, Barrande, 1874 2.) 
Fig. 27. 
Gen. Char. This genus is distinguished from Actinoceras by the 
form of the siphuncular segments, which are swollen above into a 
more or less prominent, infiated rim (fig. 27 a, r), occupying from 
about one third to two thirds of the segment, while the latter may be 
either concave (fig. 27 a) or convex below (fig. 27 c). Sometimes the 
segments are of a subturbinate form (fig. 27 h ) ; or, again, a curious 
^ Trans. Geol. Soc. ser. 2, voL i. pt. ii., 1824; explanation of plate xxviii. 
2 Syst, Sil. de la Boheme, vol. ii. Texte iii. p. 665, 1874 ; and Texte v. p. 1414 
1877. 
