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PROCEEDINGS OF THE 



[July, 1857. 



12 and 13, as well as 10 and 11 of PL 8, of the " Vierte Abhandl," 

 of the same series. The resemblance of general outline is so re- 

 markable between them, that Mr. McCrady thought it could not 

 fail to strike any one, who had the two structures presented to his 

 eye at the same time. The form of the shaft, broadest above, and 

 tapering below; the two opposite root-like processes, diverging 

 from this slender portion in each; the serrated edge of the shaft 

 is the Echinoderm larva, corresponding to the serrated edge in 

 the Graptolite, the dissepiments in the Graptolite, (fig. 4a, PI. 74,) 

 corresponding to the spaces between the bars in the Echinoderm 

 larva. 



Again, the arcuate Graptolites, which had been associated in 

 the genus Didymograpsus, most of them found their analogies 

 in nature, as at present known, only in the lyriform, calcareous 

 structure, which overarched the gullet in the larvae of Echini 

 proper. To see this resemblance, it was only necessary to com- 

 pare Muller's Sieb. Abh. PI. 1, fig. 5, PI. 2, fig. 10, PI. 8, ff, 3 

 and 8, and Vierte. Abh. PI. 7, fig. 1, 2, 5, 6, E. E., with 

 Murchison's Siluria, PI. 12, fF. 1 and la and Hisinger's Didymo- 

 grapsus geminus, Lyell Elements Geol. p. 446, fig. 600. They 

 both possessed the singular spine or thorn-like process from the 

 vertex of the curve formed by the branches. Also this structure 

 in the Echinoderm larva is not as yet known ever to possess dis- 

 sepiments like several of the other parts; the same is true of 

 Didymograpsus. 



The thorn-like process, present in other longer-shafted speci- 

 mens among Graptolites (Hall's Pal. Vol. I. PL 74, fF. 5a, 5b) 

 had also its analogy in the parts of Echinoderm larvae, and (so far 

 as was known to Mr. McCrady) in no other animal structure. 

 Gattungen der Seeigellarven pi. 1-8, passim. 



In addition to all these analogies, there was a specimen, the 

 property of the Geological Survey of Canada, which Mr. Mc- 

 Crady believed had been exhibited by Prof. Hall, at the meeting 

 of the American Association for the advancement of Science, held 

 at Providence, R. I., in 1855, and which Mr. McCrady had been 

 shown by Prof. Hall, at his study in Albany, at a later date, 

 which still preserved the Graptolitic shafts, nearly in their ori- 

 ginal normal connection with each other, and with the impression 

 of the soft membrane which stretched between them, and held 

 them together. The view of the nature of Graptolites given in 



