﻿July, 1857.] 



ELLIOTT SOCIETY. 



231 



In structure also, the Graptolites differed from the Bryozoa and 

 Hydroidea, in as much as they consisted of an internal calcareous 

 skeleton, composed sometimes of two and probably more parallel 

 bars, at times connected together by transverse bars, and of an ex- 

 ternal sheath, composed of modified organic tissue, of a horny ap- 

 pearance. On the other hand the bifurcate form of many Grap- 

 tolites and the processes before mentioned, resembling roots, are 

 points of dissimilarity with Pennatulidae. 



Again, what have been called cells may be explained upon 

 another hypothesis. 



And lastly, while no impressions of the soft bodies of the sup- 

 posititious polyps which have been imagined to fill these cells, 

 have been found, an impression of a soft fleshy structure of a 

 different kind has been found in connection with Graptolitic 

 stems. 



Prof. McCrady then stated that, in his opinon, a much greater 

 similarity existed between the fragmentary and disjointed forms, 

 which we call Graptolites and the parts of the skeletons of Echi- 

 noderm Larvae, as they had been recently made known to the 

 world, by the wonderful researches of Joh. Muller, than could be 

 found for them in any other group of known animals. 



In the first place, the thorn-like processes, the lyriform Didymo- 

 grapsus, the peculiar root-like processes of some specimens (Grap- 

 tolithus bicornis, Palaeontology of New York, Vol. I. PI. 73, fig. 

 2a, 2c, 2/,) the oval and spindle-shaped expansions of the stems 

 in others, all received an immediate explanation by this compari- 

 son, while the disjointed and fragmentary condition of the speci- 

 mens was no argument against it. The serrature of the stem, also, 

 was at least as explicable in this way as in any other, by a com- 

 parison with the toothed rods of the skeleton in the Echinoderm 

 larvae. 



The structure of the internal calcareous skeleton, which is 

 either solid, or consisting of parallel rods, which often do not unite 

 even at their very extremities, and are frequently held together 

 by transverse bars, has its exact counterpart among the Echino- 

 derm larvae. Prof. McCrady requested a comparison of the fig. 

 2a, PL 74, Vol. I. of Hall's Palaeontology, of New York, with the 

 peculiar structure figured by Muller, "Ueber die Gattungen der 

 Seeigel-larven Siebente Abhandl" PI. 6, ff. 5 and 11, separately, 

 and in ff. 4,8,9,10, in connection with other parts. Also, with ff. 



