216 T. H. Clark — New Trilobite Appendage. 



of some similar organic compound. This holds true for 

 the fossils of the black shales with which the Shumardia 

 limestone is interstratified. Without doubt the fauna of 

 the shale and the limestone was a pelagic one, well 

 adapted to a floating or a swimming existence, and pre- 

 served in such abundance in the rocks of the Levis forma- 

 tion because of the absence of any indigenous benthonic 

 predaceous or scavenging forms. The abundance of car- 

 bonaceous matter in the shales, and the absence of any 

 truly benthonic forms, indicate that the bottom of the 

 Levis sea was not capable of sustaining a fauna; this 

 would account for the preservation, almost in their 

 entirety, of many very delicate graptolites and thin- 

 shelled brachiopods. 



One of the most remarkable fossils from this horizon 

 is a single detached appendage of a trilobite. It is small, 

 less than 5 mm. in length and about 1 mm. wide. It 

 consists of the outer part of a coxopodite, a large exopo- 

 dite, a fragmentary endopodite, and one or two other 

 members to be discussed later. The accompanying figure 

 shows the disposition and relations of these parts. It 

 should be borne in mind, however, that this figure repre- 

 sents the writer's interpretation of the specimen. The 

 proximal parts are somewhat crushed, so that other inter- 

 pretations are possible. 



Fig. 1. — Sketch of the trilobite appendage from the Shumardia limestone, 

 Levis formation, Levis, Quebec. X 12. 



a. Exopodite. b. Endopodite. c. Coxopodite. d. Second coxopodite. 

 e. Second exopodite. f. ?Ventral membrane. 



The exopodite is by far the largest and the most prom- 

 inent member. Its outline is as shown in the sketch, blunt 

 at the inner end, terminating in a long spine at the distal 

 extremity, widest beyond the middle. The posterior 

 margin carries a score or so of setae, which are short, 

 stout and pointed outwards. These appear to be inserted, 

 in the margin of the exopodite, rather than outgrowths 



