Page:Smithsonian Miscellaneous Collections, Volume 85.djvu/114

Rh Apus. The elongate globular stomach (st), with the small digestive or hepatic glands (d. gl.), long simple intestine (i) terminating on the last segment at the anus (an) all suggest corresponding organs in Apus, and it is highly probable that the mouth was ventral and communicated with the stomach by a gullet extending upward and forward. The shell gland (sh. gl.) or renal organ is distinctly marked in several specimens and, as far as comparison is possible, is not unlike that of Apus.

Observations.—Waptia was a pelagic, free and active swimming animal using its abdominal limbs and the broad terminal rami for propulsion. The fact that it is found in association with algae and sponges is explained by the conclusion that the sessile forms of life were detached and drifted into the Burgess pool and deposited along with the pelagic forms that dropped to the bottom of the sea.

The carapace of Waptia is much like that of Hymenocaris except that it is not separated into two equal parts by a median longitudinal hinge line, and there is no evidence of the presence of an adductor muscle scar on each side as in Hymenocaris.

Most of the data on which the restoration is based is shown by the specimens illustrated on plates 18, 19 and 20. The form and position of the cephalic appendages are unknown with the exception of the antennae and possibly antennules; the proximal joints of the thoracic and abdominal limbs are outlined on the specimens though their form is not preserved, but otherwise the limbs are fairly well known. The body cavity is outlined by figure 3, plate 18, but it is not included in this diagrammatic figure. The shell glands (sh. gl.), stomach, intestine, and hepatic caeca are outlined, as they represent what is known of the digestive organs.

Plesiotypes.—U. S. N. M., Nos. 83948a-e.

A single specimen with a short, rounded carapace was labeled W. circularis by Doctor Walcott. As far as the rather poor preservation permits a determination it would seem that otherwise it is similar to W. fieldensis.

Holotype.—U. S. N. M., No. 83449.