Sso 



NORTH AMERICAN INDEX FOSSILS. 



Dimyarian — referring to pelecypods 

 with both anterior and posterior ad- 

 ductor muscles, as Venus. 



Dinaric — middle Triassic, general term. 



Diogenodont dentition — in pelecypods, 

 see I., 361. 



Dis — a prefix meaning separation or 

 signifying not. 



Disciform — disk-shaped. 



Discinoid — resembling Discina. 



Discoid — shaped like a disk ; coiled in 

 one plane (see Fig. 1206). 



Dissepiments — in graptolites and bryo- 

 zoans, the cross bars uniting the 

 branches. In corals, the horizontal 

 or oblique plates uniting the adjoin- 

 ing septa ; as seen in transverse sec- 

 tion, they are usually curved or irreg- 

 ular between the septa (see Figs. 32, 

 loi). 



Distal — remote from the point of at- 

 tachment or center. 



Distichals — in crinoids, the second se- 

 ries of arm plates or brachials, situ- 

 ated above the axillary costals (see 

 Fig. 1907, D). 



Divaricate — to branch. 



Divaricators — the opening muscles of 

 brachiopods. Also called diductors. 



Dolomite — a mineral consisting of car- 

 bonate of lime and magnesia. 



Dorsad — toward the dorsum or back ; 

 backward. 



Dorsal — pertaining to the back. 



Dorsal cup — in crinoids, the crown 

 exclusive of the arms and tegmen. 

 Dorsal furrows — in trilobites, the two 

 grooves limiting the glabella and 

 axis laterally. 

 Dorsal shield — in trilobites, the en- 

 tire dorsal test, inclusive of cepha- 

 lon, thorax and pygidium (see Fig. 

 1542). 

 Dorsal valve — in brachiopods, the 

 brachial valve. 



Dorsocentren — see Fig. 1231. 



Dorsum — the back. In most cephalo- 

 pod shells, the interior of the coil ; 

 in insects, see II., 420. 



Doublure — the infolded margin of a 



trilobite test ; this produces the hol- 

 low spines from the ends of the genal 

 angles, the segments and the pygi- 

 dium (see Figs. 1556, e, 1559). 



Douglas formation — upper Carbonic of 

 Kansas. 



Dresbach shale — a subdivision of the 

 St. Croix formation. 



Dudley formation — middle Carbonic of 

 Kansas. 



Dundee limestone — middle Devonic of 

 Michigan. 



Dunkard formation — Permic of eastern 

 United States. 



Duplin beds — upper Miocenic of North 

 Carolina. 



Dysodont dentition — in pelecypods, see 

 I., p. 361. 



Eagle Ford formation — lower Cretacic 

 (Coloradoan) of Texas. 



Eagle Pass formation — see Navarro 

 formation. 



Ear — in pelecypods, the anterior car- 

 dinal expansion of the shell, usually 

 smaller and more distinctly defined 

 than the posterior expansion or wing. 



Eccentric — not centrally placed. 



Ectoderm — the outer cellular body layer. 



Eden formation — lower Cincinnatian 

 (upper Ordovicic) of eastern U. S. 



Edwards limestone — middle Comanchic 

 (Fredericksburgian) of Texas. 



Elbrook formation — middle Cambric of 

 Pennsylvania, Maryland, etc. 



Eldon formation — middle Cambric of 

 the Canadian Rockies. 



Ellis formation — Jurassic of Yellow- 

 stone region. 



Elmdale formation — base of Permic in 

 Kansas. 



Elvins formation — upper Cambric of 

 Ozark Mountains. 



Elytra — in beetles, the horny sheaths 

 concealing and protecting the softer 

 posterior wings (see 11. , 424). 



Emarginate — with a notched margin. 



Embryonic — referring to the earliest, 

 undeveloped stage of an animal, after 

 the egg stage (see also Ontogeny). 



I 



