On CalamoporcB in gravel deposits near Ann Arbor, Mich. 395 



limetres wide, and others ia all gradations down to tubes of one 

 millimetre, or even less, are equally common. 



A certaia size of tubes is always predominant in specimens, 

 but smaller and larger ones are found intermingled. Exteriorly 

 the tubes are smooth, or marked with transverse lines of growth, 

 polygonal ; interiorly, frequently rounded, with from 12 to 14 

 Imear longitudinal sulci, including in this number the lines 

 formed by the angles of the polygons. Most characteristic of 

 this species are horizontal, or variously oblique or flexuous, lin- 

 guiform lamellae, which project from the side-walls of the tubes 

 m various degrees of development and of multitude. 



These lamellae are perfect analogues of the spinules of the 

 above described species from the Niagara group, and must not 

 be confounded with the ordinary diaphragms, although they can 

 take their place and function. 



In some specimens regular diaphragms divide the tubes, and 

 the intervals between them are found either studded with shorter 

 lamellae, or interrupted by partial compound diaphragms, formed 

 by the enlarged and coalesced lamelliB. In other specimens no 

 regular simple diaphragms can be found, and the irregularly 

 coalesced laraellse replace them altogether; but even in those 

 specimens in which, at certain periods of growth, no regular 

 diaphragm can be noticed, successively, or abruptly, the tubes 

 may alter their appearance, and, for a while, only regular simple 

 diaphragms may be seen, with the intervals between them en- 

 tirely smooth. This circumstance proves satisfactorily that the 

 different degrees of development of these organs, far from being 

 of generical importance, are not even constant in the prolonga- 

 tion of one and the same tube. 



In some specimens the lateral lamellw form twelve tolerably 

 regular longitudinal rows, which are separated by the longitu- 

 dinal furrows, but in other specimens smaller and larger la- 

 mellae, horizontal, oblique, or flexuous, are dispersed in per- 

 fect disorder, forming by their coalescence a coarse cellular 

 tissue, rather than a series of diaphragms. The diaphragms 

 formed of lamellas more equal in size and position, have a stel- 

 late surface, from the cicatrices indicating the outlines of the 

 component laraellee. Milne Edwards, probably having in view 

 this kind of diaphragms, speaks of " 12 vertical lamellae reach- 

 ing to the centre of the tabulae," but the vertical lamella3 and 

 the tabulae are in this case one and the same thing. 



The pores form from 8 to 12 rows on the circumference of a 

 tube, are large and numerous; surrounded by a prominent rim, 

 or not. They seem to be more numerous' in the tubes with 

 complicated diaphragms, than in those which have them more 

 simple. 

 Am. Jour. Sci.-Second Sekies, Vol. XXXIY, No. I02.-Xov., 1862. 

 51 



