186 
N-ATJTILOIDEA. 
Horizon. Niagara Group (Wenlock). 
Locality. Drummond Island, Lake Huron. 
Eepresented by the type specimen figured by Stokes. 
Actinoceras spheroidale^ Stokes, sp. 
1824. Huronia sj^heroidalis, Stokes, Bigsby, Trans. Geol. Soc. ser, 2, 
Aol. i. pt. 2, p. 203, and “Explanation of Plates,” pi. xxviii. f. o. 
1840. Huronia Portlockii, Stokes, ibid. vol. y. p. 710, pi. lx. f. o. 
1866. Orthoceras {Huronia) Portlocki, Barrande, Syst. Sil, de la 
Boheme, yol. ii. Texte hi. 1874, p. 741, pi. ccxxxii. f. 4. 
1866. Orthoceras {Huronia) spheroidale, Barrande, ibid. p. 742, 
pi. ccxxxii. f. 3. 
Sjp. Char. Shell straight. Section probably circular. The rate of 
increase may be roughly estimated at about 1 in 9. The septa, 
which are seen only as faint lines upon the surface of the rock, are 
distant about 8 lines, where the shell has a diameter of 2^ inches. 
The siphuncular segments are of the form of flattened spheroids, 
the ratio of the vertical to the transverse diameter bciog nearly 
as 6 : 17. The foramina through which the tubuli 'thrown oflP by 
the endosiphon opened into the septal chambers are plainly dis- 
cernible in one of the specimens ; they consist of a row of minute 
apertures encircling transversely each siphuncular segment, their 
position being along a line a little above the greatest convexity of 
the segment. Nothing whatever is known of the test of this 
species, the specimens representing the latter consisting only of 
internal casts. 
Remarks. In the specimen hitherto known as Huronia Portlockii^ 
the siphuncle has been crushed so as to cause its several elements to 
appear narrower than they were originally. The specimen of 
A. spheroidale (the type) shows the segments of the siphuncle in 
what is probably their natural shape. This specimen also exhibits a 
transverse section of the endosiphon. 
Barrande compared the present species with A. roiM/nfwm, Billings, 
but it is distinguished from the latter not only by the horizontality 
of its siphuncular elements, which are oblique to the long axis of 
the shell in Billings’s species, but also by the much greater distance 
separating the septa. 
A. spheroidale is distinguished from A. ClouH, Barrande, with 
which that author compares it, by the same characters that separate 
it from A. rotulatum, Billings. Moreover, A. Clouei is alleged to 
be derived from rocks (in Newfoundland) which are of Ordovician 
age (Barrande’s Second Eauna), and probably belong to the first 
stages of that system. 
