62 [S 



ENATE 



in these forms indicates that the cells increase by lateral extension; and a single 

 fragment in the collection gives some evidence of four rows of reticulations, as in 

 other forms of the genus. It is not improbable, also, that in entire specimens we 

 may find evidence of a central axis; since the implied mode of growth, in its simi- 

 larity to that of the graptolites, indicates this structure. 



GENUS THAMNOGRAPTUS ( n.g.). 

 Bodies consisting of straight or flexuous stipes (simple or conjoined at the base?), 

 ■with alternating and widely diverging branches : branches long, simple or ra- 

 mose in the same manner as the stipe. Substance fibrous or striate; the main 

 stipe and branches marked by a longitudinal central depressed line, indicating 

 the axis. Cellules or serratures unknown. 



These bodies are associated with the Graptolites; and from a general similarity 

 in their substance, I suppose them to belong to the same family of fossils. In all 

 the specimens the surface visible is smooth or striated without indentations, and 

 marked by cross fractures or cleavage planes. The fragments of what appear to 

 be carbonized plants, in the shales of the Hudson-river group, probably all belong 

 to this genus, or to the Dendrograptus. 



THAMNOGRAPTUS TYPUS(n.s.;. 

 Stipe strong, flattened : branches alternating, about half as wide as the main 

 stipe and expanding at their junction with it, simple, marked along the centre 

 by a depressed line or axis. Surface marked by fine longitudinal striae, with 

 obliquely transverse fractures or lines of cleavage. 



Fig.l. 



The accompanying figure is from a 

 fragment of this species, of the natural 

 size. 



Geological position and locality. In 

 the shales of the Hudson-river group : 

 Near Albany. 



Thamnogeaptus typus. 



This genus was proposed by me in 1858, in a paper read before the American 

 Association for the Advancement of Science; but no publication has been made of 

 the name, so far as I know, except in a newspaper report at the time. At that time 

 I had seen but a few fragments of the species, the first one having been discovered 

 by Mr. J. B.Ellis of Albany; and it is only since the descriptions were in type 

 that the specimen, from which the accompanying figure 2 has been made, was 

 discovered by Mr. Whitfield among the shales at Normanskill. The constancy of 

 the generic characters in two distinct species, and in at least half a dozen speci- 

 mens, affords satisfactory evidence for separating this from any described forms. 



