PTEROPODA. 187 



COLEOLUS ACICULUM. . 



PLATE XXXII A, FIGS. 11-15 (16?). 

 Orthoceras acictdum. 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 striae. 



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 similarityof form and proportions, I had compared them with Coleolus 

 tenuicinctum, 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 Genesee slate, as shown in figure 13. 

 These slender bodies in the Portage group are doubtless identical with the one 

 d e scri bed 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. tenuicinctum ; 

 but in the absence of evidence of absolute identity, I leave them under the 

 original specific designation. The following forms, figured on plate XXXII 



