200 BULLETIN OF THE 



imprints as though it had contracted or shrunk after the decomposition 

 of the muscles forming the leg. 



That such a delicate membrane as enclosed the appendages and 

 ventral surface of the Trilobite may be preserved so as to be observed 

 in the fossil state, there is little doubt. It may be an impression in 

 fine, smooth shale, or by the replacement of the parts by a mineral 

 differing in color from the matrix, so as to show them distinctly. In 

 Eocene fresh-water strata on the Isle of Wight the gill feet of Branchi- 

 pus have been found. They were in a fine argillaceo-calcareous rock 

 and stained with iron so as to show as well as in a photograph.* It 

 is difficult to conceive of a more delicate test of the preservation of 

 the branchiae, and other parts liable to destruction from their nature, 

 than this. 



The Intestinal Canal. — Attention was first called to the existence 

 of the intestinal canal in the Trilobite by Prof. Beyrich, who discovered 

 it in a specimen of Trinudeus ornatus.-f M. Barrande subsequently 

 gave numerous illustrations of its preservation in Trinudeus Goldfussi, 

 where, he says, it extended from the middle of the glabella along the 

 interior of the median lobe to the extremity of the pygidium. In some 

 examples it is filled with very fine, soft clay. This substance has, per- 

 haps, largely contributed to preserve the form of the canal, which, once 

 filled and buried in incompressible sand, has undergone no other de- 

 formation. There must have been some peculiarity of conformation 

 that preserved the intestinal canal in this species, as in other Trilobites 

 from the same quartzites no traces of it are to be seen. J M. Barrande 

 mentions that Dr. A. de Volborth discovered in an Illcenus a length- 

 ened and articulate organ which originated in the glabella and became 

 attenuated towards the pygidium. § A cast of the interior, as shown 

 in Plate IV. fig. 7, might have such an appearance. This, however, 

 is conjectural, as I have not seen an illustration of Dr. Volborth's 

 specimen. 



In cutting sections of Trilobites it was a very rare occurence to find 

 traces of the intestinal canal. One specimen out of one hundred was a 

 large proportion. The visceral cavity was usually filled witli calcspar, 

 and all vestiges of the canal or any other organ obliterated. 



In a note taken while cutting sections in December, 1876, it is 

 stated that when grinding down a section from the anterior towards 



* Nature, p. 381, 1877. 



t Uel). Triloh., IL Stuck., p. 30, Plate IV. fi;^. 1, r, 1846. 



X Sys. Sa. Boh., I. p. 229, 1852. § Ibid., II. p. 182, 1872. 



