Page:Walcott Cambrian Geology and Paleontology II.djvu/187

NO. 5 tube is usually so completely flattened that the fine concentric lines and fine ridges that give an annulated appearance to it have disappeared; often the tubes appear to be longitudinally striated as the result of lateral compression. Some tubes appear to be slightly constricted near the aperture and also a little thickened. The tubes were thin and easily compressed and flattened. They may have been calcareous, but from their bright, almost shiny, luster they were more probably chitinous or parchment-like.

Dimensions.—The largest flattened tube has a length of 68 mm., with a width of 12 mm. at the larger end, and of 8 mm. at the smaller. A more slender tube 64 mm. long is 9 mm. wide at the large end and 2 mm. at the smaller. The larger number of tubes have a transverse diameter of from 5 to 7 mm. at the larger end.

Animal.—Ten specimens show more or less of the animal projecting from the tube. It fills the end of the tube and is divided into sections a little longer than wide that are faintly indicated by slight successive contractions, and the presence of somewhat more prominent spines or hooks. The spines appear to have been arranged in concentric rows over all parts of the surface of the body except the terminal section. A specimen that is not illustrated shows a conical terminal section with several small-jointed appendages about its posterior end. My present impression is that the terminal section represents the head and the appendages a circle of gills. From the fact that the animal projects so much more from some tubes than it does from others, it seems that it was retractile and could withdraw into its tube. No traces of an operculum have been seen. With the somewhat formidable series of spines to protect it an operculum would scarcely have been necessary.

Observations.—On pl. 19, fig. 7. there is inserted for comparison with Selkirkia major a photograph of a specimen of Hyolithes carinatus Matthew showing the triangular tube, operculum, and, for the first time among the Hyolithidæ, the curved supports of the fins of a pteropod.

The discovery of the animal that lived in one of the tubes that has been classed with the pteropods removes one more doubtful form from the latter to the annelids, and with it will probably go Hyolithellus and other tube-like shells that have none of the distinctive external characters of Hyolithes and its allies.

In these preliminary notes I do not care to mention further the relations of the various Paleozoic tube-like fossils that have been referred to the Pteropoda and Annelida, except to call attention to a