10 PALAEONTOLOGY OF NEW YORK. 



The forms des&ribed us T. tenuistriatus, T. Oswegoensis, T. Sterlingensis,* and T. 



Rirhmondtnsis;\ are rarely if ever quite straight, and are usually considerably 

 curved, a feature unknown among the most characteristic forms of the genus 

 I i i.itks. The T. incurvus of Shumard, now recognized as from the same 



horizon, is a curved form, as the name implies. We have at the outset, there- 

 fore, in all these species, to recognize a deviation from the acknowledged char- 

 acteristics of Tentaculites as described by the best authors and as known to us 

 in American and European rocks. These forms in their intermediate stages 

 are sharply annulated, and, in their advanced stage of growth, always longitu- 

 dinally striated in a manner not observed among true Tentaculites. Farther 

 observation shows that in their young state they are parasitic, often occurring 

 in groups, with their bases in contact and attached to some foreign body, as a 

 shell or a fragment of a crinoid column ; and that the extreme basal portion or 

 initial point, in the young state, is always curved, often to a full volution; but 

 this portion becomes absorbed, dissolved or worn off as the animal increases in 

 size and the tube assumes a more or less direct manner of growth, continuing in 

 a straight or slightly flexuous line and gradually enlarging toward the aperture. 

 These tubes which in their beginning are apparently smooth, gradually become 

 annulated and finally striated longitudinally. It usually and perhaps always 

 happens, however, that during some stage of their growth, not always depend- 

 ing on the age, the walls become thickened and the annulations obsolescent. 

 < >ccurring either singly or in groups, wherever the surface of attachment is broad 

 enough to admit of it, they continue adherent until they have attained a con- 

 siderable size — that is, a length of 20 to 35 mm., or even more. The apertures 

 in nearly all examples are apparently incomplete, or with the margins broken. 



The phases here described are illustrated in figures 1-11 of plate cxv. 



I nder other circumstances, where apparently the conditions have been un- 

 usually favorable, these colonies, adherent to some other body at their bases 

 only, continue to increase in length and diameter; the lateral walls from being 

 simply in contacl become coalescent, and they continue this growth till the form 



s of the Academy of Sciences, Philadelphia, and Report Geological Survey of Illinois. 

 vol. iii. 



\. Miller, Cin. Quart. Jour. Sci. 1874. 



