372 NORTH AMERICAN INDEX FOSSILS. 



of overlapping plates, two of large and equal size and two others 

 small and unequal; Examples: 6. S. spinigera Clarke, of the Ham- 

 ilton shales of New York (Fig. 1672). IV., Scalpellum Leach 

 (Cretacic-Recent) of twelve to fifteen variously formed shelly 

 pieces; Examples: 7. S. conradi Gabb from the Jerseyan beds of 

 New Jersey. V., Squama Logan (Cretacic) ; Examples: 8. S. 

 spissa Logan, adhering to shells of Inoceramiis by the entire 

 length, and found in the Coloradoan of Kansas; 9. S. lata Logan, 

 from the same beds. VL, Stramentum Logan (Cretacic) ; Ex- 

 ample: 10. S. haworthi Williston, attached to Ostrea congesta by 

 the peduncle and found in the Coloradoan of Kansas. VIL, Bala- 

 mis Lister (Eocenic-Recent), the true acorn barnacle with six 

 pieces to the corona, and a pair of scuta and tcrga closing the 

 aperture, and generally lost in fossil forms; Examples: 11. B. 

 concavus Bronn (Fig. 1673) (Miocenic-Recent), on both Atlantic 

 and Pacific coasts, and in Europe. YIIL, Protohalanus Whitfield 

 (Devonic) with twelve plates to the corona, and IX., Palceocreusia 

 Clarke (Devonic) a one-piece shell with deep, cylindrical base, and 

 generally embedded in corals (Favosites). Example: 12. P. de- 

 vonica Clarke, Onondaga of New York. 



Subclass Malacostraca Latreille. 

 Order PHYLLOCARIDA Packard. 



Crustacea with the body composed of five cephalic, eight thoracic 

 and two to eight abdominal segments. Head and thorax covered 

 by a thin chitinous or partly calcareous, single or bivalved shell or 

 carapace. When bivalve, the valves are separated by a straight, 

 unarticulated, single or double hinge. In front of the carapace is 

 a narrow movable plate or rostrum. The head bears two pairs 

 of antennae and stalked compound eyes. Abdomen composed of 

 ring-like segments and often ending in a spine-like tail-plate (tel- 

 son), provided with lateral spines or cercopods. In this order are 

 provisionally placed the two doubtful genera Stenotheca and Ri- 

 beiria, the crustacean character of which is not universally ad- 

 mitted. Only the " carapace " is known in these types. 



