Page:Walcott Cambrian Geology and Paleontology II.djvu/89

 the material now available it is not perfectly clear how many of the "peltato-digitate" tentacles originally existed. Two only have thus far been seen on each of several beautifully preserved specimens. It may be that five will be found, two of which will be fully developed and three immature or atrophied.

The constriction indicating the œsophagus is present in many specimens. In fact, the canal always narrows at this point even though the oral chamber is not expanded in front of it. The elongated constriction of the œsophagus is well shown by text fig. 5.

The stomach is the prominent and best preserved part of the animal. It occupies the largest part of the alimentary canal and appears to have had strong, more or less corrugated walls, and invariably to contain traces of the food in it at the time of the animal's death. This is shown by nearly all of the figures on plates 8-12. The length of the stomach is indicated by figs. 1 and 4, pl. 9; fig. 2, pl. 10; and figs. 1 and 2, pl. 12. Side views of the compressed stomach are shown by fig. 3, pl. 9; and figs. 1 and 2, pl. 11.

The strong walls of the stomach are indicated by fig. 2, pl. 10, also by the fact of its preservation when the remaining portions of the animal have disappeared. Upward of two hundred specimens, in various conditions of preservation, were found in the collections of 1910, and in all of these the stomach was clearly defined. In the simplest form only the outline of the stomach was preserved (fig. 3, pl. 10; and figs. 1 and 2, pl. 12), but there are all the gradations between this and instances where nearly the entire animal is preserved (fig. 3, pl. 8; and fig. 5, pl. 9).

The posterior end of the stomach is located where the alimentary canal usually contracts abruptly in size and the shiny area of the stomach terminates. This is illustrated very definitely by fig. 2, pl. 10; also by figs. 1 and 4, pl. 9; and figs. 1 and 2, pl. 12.

The intestine is usually as long as and less than one-half the diameter of the stomach. In some examples the canal shows traces of matter inside of it (pl. 9, fig. 1; and pl. 10, fig. 2). The intestine contracts at its posterior end (pl. 12, figs. 1 and 2), but as yet the actual anal aperture has not been observed.

Genital organs.—The only suggestion of a genital organ is shown on fig. 5, pl. 9, at (g) where a three-lobed body is pressed in with the subumbrella surface.

Dimensions.—The largest specimen is represented by fig. 3, pl. 12. The right and left sides have been partly folded under and lost, but by taking the average width of the lobed umbrella outside of the