PTEROPODA. 
187 
COLEOLUS ACICULUM. 
PLATE XXXII A, FIGS. 11-15 (16?). 
Orthoceras aciculum, Hall. Geol. of N. Y. Surv. Fourth Geolog. Dist., p. 243, fig 4. 1843. 
Fossil extremely elongate, cylindro-conical, having in the larger specimens a 
diameter at the base (in its flattened condition) of about seven millimetres, 
with a length^of more than three inches, becoming extremely slender and 
attenuate towards the apex. 
These fossils usually appear to have been subjected to maceration in the 
muddy sediment, and seldom preserve any indication of surface-markings. 
There are rare examples, which present some evidence of obscure annulations 
or strise. 
The specimens are usually much compressed and entirely inseparable from 
the surrounding shale, and so destitute of external characters that they could 
not, by themselves alone, be referred to any known organic forms. From their 
general similarity of form and proportions, I had compared them with Coleolus 
tenuicindum, while one or two specimens of recent acquisition, from the shales 
of the Portage group, which are apparently referable to the same form, pre¬ 
serve some obscure surface-markings. 
These fossils occur in the Genesee slate, and in the olive shales of the Portage 
group; in the latter formation appearing usually as the slender attenuate bodies 
represented in figure 14 of plate XXXII A. Similar slender forms also occur 
with the more elongate ones in the Geneses slate, as shown in figure 13. 
These slender bodies in the Portage group are doubtless identical with the one 
described by me as Orthoceras aciculum ut cit. The original of this species 
is not now accessible to me; but an examination of all the similar forms in 
the same formation shows them to be destitute of septa, and therefore not 
referable to Orthoceras. 
It is with much hesitation that I separate these forms from C. tenuicindum; 
but in the absence of evidence of absolute identity, I leave them under the 
original specific designation. The following forms, figured on plate XXXII 
