Page:Walcott Cambrian Geology and Paleontology II.djvu/193

NO. 5 1911 material will be discovered that will give much better data for determining its family relations.

Formation and locality.—Middle Cambrian: (35k) Burgess shale member of the Stephen formation, west slope of ridge between Mount Field and Wapta Peak, one mile (1.6 km.) northeast of Burgess Pass, above Field on the Canadian Pacific Railway, British Columbia, Canada.

"The Gephyrea are marine Annulata devoid of any trace of segmentation in the adult condition, without parapodia, and either without setæ or with only a limited number; with either an invaginable anterior body region or introvert, at the extremity of which is the mouth surrounded by tentacles, or with a long, highly retractile proboscis representing the pre-oral lobe of the larva, and having the mouth situated at the base. The anus is sometimes terminal and posterior, sometimes anterior and dorsal. There is an extensive cœlome filled with a corpusculated fluid, and not divided by septa. The ventral nerve-cord is not made up of a series of ganglia. There is, as a general rule, only a single pair of nephridia. The sexes are separate; the ovaries and testes simple masses of cells; the nephridia act as reproductive ducts. The larva is a trochophore."

The genus Ottoia is tentatively referred to the Gephyrea, since, while it possesses certain characters of the Gephyrea, it has others that do not come clearly within the class. The segmentation of the body serves to withdraw it from Gephyrea, but in so ancient a form this character is to be anticipated. The proboscis is similar in function to that of some of the Gephyrea and Polychæta where the buccal region is "everted" and may be withdrawn into the buccal region. The proboscis and mouth of Ottoia also suggest the sucker-like mouth and proboscis of some of the Hirudinea (leeches). The exterior appearance of the body of Ottoia is also not unlike that of some of the leeches that have a slender body, finely marked segmentation, and a retractile proboscis with the mouth at the end. The absence of parapodia removes Ottoia from the Polychæta, and the presence of segments is not sufficient to place it with the Hirudinea.