TUBICOLAR ANNELIDA. 13 



sents all the phases of development from the convolute, spirorbiform condition 



to the nearly straight forms, and all have a very similar aspect to the speci- 

 men represented in figures 1 and "J of the same plate. We know it only in it- 

 immature condition, in the single specimen illustrated. 



In figure 41 the tubes are somewhat more slender and more flexuous than in 

 specimens of the same degree of development from the region around Cincin- 

 nati, and this form will probably prove a, distinct species. The figure is from 

 the original specimen, described as Tentaculites? flexuosus, from the Trenton lime- 

 stone (Pal. N. Y., vol i, p. 92, pi. xxix. figs. 6a-d). Want of material will 

 prevent a complete comparison and final discussion of the relations of this 

 species with any other, at the present time. 



The forms illustrated on plate lxxii, figs. 2 a and b, Pal. N. Y., vol. i, p. 284, 

 were referred to the species Tentaculites [/J flexuosa, the ? after the generic 

 name being accidentally omitted. A comparison was also suggested with Cor- 

 nulites serpularius, Schlotheim (Murchisoifs Sil. Syst., p. 627, pi. xxvi, figs. o-8). 



The specimens from the Hudson River group of New York are, however, 

 more slender and are frequently regularly curved, not flexuous as in the typical 

 form of T. ? flexuosus, from the Trenton limestone. They are very similar to, 

 and perhaps identical with those from the same horizon in the west, and their 

 probable identity with the western forms was at that time recognized in citing 

 the localities. 



W e come now to consider some forms of this genus known to us in the 

 higher rocks, and more especially the single species occurring in the Niagara 

 group at Waldron, Indiana. The material at hand is not so complete in some 

 respects as that from the Hudson River group of the Cincinnati region, repre- 

 sented on plate cxv. In its entire aspect, however, it presents the same phases 

 of development, and we have more complete material to illustrate the advanced 

 stages of growth in this species. The earliest condition in which their specific 

 relations usually are observed, is that of groups of slender, flexuous, or rarely 

 almost straight tubes, attached on one side for nearly or quite their entire length 

 to some other organisms, as the shell of a Brachiopod, a Gastropod, or the calyx 

 of a Crinoid. In this condition the apertures are frequently turned outward. 



