Page:Walcott Cambrian Geology and Paleontology II.djvu/51

 edge of its inner third, or they may be of a lamellated structure as shown by fig. 1, pl. 3, fig. 1, pl. 2, fig. 3, pl. 6. What is now known of these branchial clusters recalls very strongly the lamellated branchial fringes occurring in the cephalic portion of the trilobite Calymene senaria and in specimens of Neolenus serratus (see pl. 6, figs. 1 and 2) associated with Sidneyia inexpectans.

Observations.—In this preliminary notice of this remarkable crustacean I have not attempted to describe many minor features of the ventral appendages of the cephalo-thorax and abdomen. The combination of characters shown by the conformation of the dorsal shield and the grouping of the appendages indicates quite clearly a transition form between the Trilobita and Eurypterida. In view of larger collections being made available during the season of 1911 further description will be deferred.

Formation and locality.—Middle Cambrian: Stephen formation, Ogygopsis shale on west slope of ridge between Mount Field and Mount Wapta, about 3800 feet above Field on the line of the Canadian Pacific Railway, British Columbia, Canada.

What is known of this genus is contained in the description of the type species. It differs markedly in form and surface from Sidneyia. From Pterygotus, Eurypterus, and other genera of the Eurypterida it differs in the character of the surface, epistoma, and abdominal segments.

Genotype.—Amiella ornata Walcott, which is associated with Sidneyia inexpectans in British Columbia.

The generic name is given in honor of Dr. Henry M. Ami, of the Geological Survey of Canada.

Of this species only one broken specimen of the dorsal shield is known. This shows that the body was elongate, narrow, and the abdomen formed of a number of large segments of which remains of seven are preserved; also a part of the cephalo-thorax.

Crust thin and compressed in the shale.

Cephalo-thorax.—The portion of the cephalo-thorax preserved (it may be only the epistoma) has been turned about, the dorsal shell of the cephalo-thorax having been loosened and displaced. If it is