78 SIXTEENTH REPORT ON THE CABINET*OF NAT. HISTORY. 



These expansions consist of two thin films, which, even in their 

 compressed condition, are found to be separated by a filling of 

 shaly matter ; and in some of the larger ones, this interspace 

 appears to have been filled with small shells, or fragments of 

 shells, of the Genus Amboccelia, reminding one of the spiral sacs 

 of Pyrula. 



These bodies have grown only in quiet positions, as proved by 

 the fine shaly and slowly deposited matter which envelops them. 

 After examining many of the fragments, which present a great 

 variety of form and proportions, the conclusion is inevitable that 

 they have all grown as here described, and that these large and 

 variously shaped remains are either the higher and last growth 

 which has not maintained the circular form, or that they are 

 detached portions which have been distorted by pressure after 

 their separation. 



The term Fucoides, which is applied to these as well as to other 

 very dissimilar bodies of marine origin, should give place to some 

 more definite and distinguishing term ; and I would .propose the 

 name Spirophyton. 



GENUS SPIROPHYTON ( n.g.). 



Fossil marine plants, consisting of broad, thin, striated or fascicu- 

 late, ridged or corrugate fronds or discs, which grow in a spiral 

 form, and increase by the extension and expansion of the frond 

 in a spirally ascending direction. 



These fronds, in single detached volutions, present a concave 

 upper surface, with a corresponding convexity of the lower surface, 

 and usually a little thickened at the central axis. The surface is 

 finely striate, wrinkled, or fasciculate ; the outer margin strictly 

 defined, or irregular in the different forms. The degree of concavity 

 of the spiral, as well as the superficial character, varies in different 

 species. 



The fossils of this type are remarkably characteristic of the Devonian 

 strata, or of those groups beginning with the Upper Helderberg, and in- 

 cluding all the intervening strata to the Carboniferous system ; and they 

 may likewise exist above and below these limits.* 



From the materials before me, I am able to recognize the following 

 species : 



* I have a well-marked species of the genus from a short distance beneath the Coal 

 conglomerate of Ohio. 



