NO. 6 MIDDLE CAMBRIAN BRANCHIOPODA, ETC. 183 



Hymenocaris Salter, 1866, Mem. Geol. Survey Great Britain, Vol. 3, p. 293, 

 pi. 2, figs. 1-4, pi. 5, fig. 25. (Description of genus slightly changed and 

 illustrations given of type species.) 



Hymenocaris Etheridge, 1881, iMem. Geol. Survey Great Britain, Vol. 3, 

 '2d ed., p. 484. (Reprint of description by Salter, 1866.) 



The generic description by Salter ( 1866) is as follows : 



Carapace ample, semi-oval, narrowed towards the front, curved downward 

 at the sides, but not angularly bent along the dorsal line ; no external eyes ; 

 antennae?; abdomen as long or longer than the carapace, of nine transverse 

 segments, the last with three pairs of unequal lanceolate appendages. 



The illustrations accompanying the description by Salter show the 

 general form of the carapace and abdomen. These taken in connec- 

 tion with seven specimens of the carapace, two of which have several 

 segments of the abdomen attached to them (in the collection of the 

 United States National Museum), enable me to identify the genus 

 and add materially to the description of Salter. 



On one of the specimens of the carapace [Salter, 1866, pi. 2, fig. 3] 

 two antennae are shown, otherwise no traces of the appendages of 

 the head or body are mentioned. 



'Hymenocaris perfecta (pi. 31, fig. 2) shows the antennae to be 

 jointed, while the antennae noted by Salter for Hymenocaris vermi- 

 caiida were unjointed. 



The genus and its type species have been referred to by authors 

 many times during the past fifty years, and Salter's diagrammatic 

 figure has been copied into nearly all text-books in which the fossils 

 of the Cambrian system are illustrated. 



In addition to those described in this paper there are a number of 

 American species of Hymenocaris known. These include H. argentea 

 (Walcott)' from the Middle Cambrian of Utah, and several un- 

 described species from the Middle Cambrian of the Cordilleran pro- 

 vince of western North America. 



The valves of the carapace of Iso.vys acutangula' (Walcott) are 

 abundant in the lower portion of the Burgess shale, and there are 

 also fragments of the carapace of a very large form that possibly may 

 be related to Hurdia victoria (pi. 32, fig. 9). 



HYMENOCARIS PERFECTA, new species 



Plate 31, figs. 1-6 (upper specimen) 



The form and outline of the carapace are shown as flattened on the 



shale by figure i on side view and somewhat roughly from dorsal view 



by figure 2. Several specimens show seven abdominal segments 



' Bull. U. S. Geol. Survey, No. 30, 1886, p. 146, pi. 8, fig. 5. 

 * Canadian Alpine Journ., Vol. i, No. 2, 1908, pi. 2, fig. 5. 



