184 
KAFTILOIDEA. 
ActinoceraS) sp. 
1878. Orthoceras imh'icatum, Etheridge {non Wahlenberg), Quart. 
Journ. Geol. Soc. vol. xxxiv. p. 607 (pars). 
This specimen (labelled D 12) was placed by Mr. Etheridge under 
the name Orthoceras imbricatum, together with the one I have identi- 
fied as Orthoceras Darwini^ Billings (^q. v.). It is a fragment of the 
septate portion of the shell much eroded, but showing traces of a 
siphuncle inflated between the chambers, so that there appears to be 
ground for regarding it as an Actinoceras. The septa are very ap- 
proximate, their distance but slightly exceeding -h the diameter of 
the shell. The rate of increase may be roughly computed at about 
1 in 5. 
Horizon. Magara Group (Wenlock). 
Locality. Dobbin Bay, Smith Sound, Arctic America. 
Bepresented by a single specimen in the Collection. 
Actinoceras Whitei, Stokes, sp. 
1824. OrthocercB , Bigsby, Trans. Geol. Soc. vol. i. pt. 2, 
p. 204, pi. XXX. f. 2. 
1840. Ormoceras Whitei^ Stokes, Trans. Geol. Soc. ser. 2, vol. v. pt. 3, 
p. 709, with a reference to Bigsby’s figures (loc. cit.). 
1870. Orthoceras Backi, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte iii. 1874, p. 731, pi. ccccxxxvii. ff. 17, 18. 
Sp. Char. Shell straight. The transverse section cannot be de- 
termined from the fragments of the species known. The septa are 
regular and horizontal, and distant about the diameter of the 
shell. The siphuncular bulbs are much inflated between the 
chambers, the relation of the height of a given bulb or segment to 
its breadth being as 4:7. In one of the specimens figured b}" 
Barrande {loc. cit. fig. 18) the endosiphon is delineated in two or 
three of the siphuncular segments which have been broken open. 
The foramina by which the tubuli of the endosiphon communicated 
with the septal chambers are noticeable in Stokes’s type specimen. 
Nothing is known of the su^rface of the test. 
Jtemarks. The fossil figured by Barrande (belonging to the Natural 
History Society of Montreal) was communicated to him by Billings, 
who suggested its identity with A. Whitei, Stokes, and I am quite 
in accord with this view of its affinities. It is clearly distinguished 
from A. Backi, to which Barrande refers it, by the form of its 
siphuncular elements, which are more globular than they are in the 
latter species ; this also causes a greater’ space to intervene between 
the septa. 
