GLOSSARY. 



829 



Cystiphragm — a strongly curved plate 

 extending only partly across a zoe- 

 cium. These are usually confined to 

 the margins, with diaphragms in the 

 center of the zoecial tube (see Fig. 

 186, c', d). 



Cystose — containing or resembling a 

 cyst or bladder. 



Dactylopodite — see II., 388. 

 Dakota sandstone — basal Cretacic sand- 

 stone of central North America. 

 Daonella beds — middle Jurassic of Ne- 

 vada. 

 Dayton limestone — Niagaran of south- 

 ern Ohio. 

 Deadwood formation — upper Cambric 



of Black Hills, etc. 

 Decewville beds — upper Oriskany of 



western Ontario. 

 Decker Ferry formation — upper Siluric 



of New Jersey, Pennsylvania, etc. 

 Deepkill shale — lower Ordovicic of 



Hudson Valley. 

 Deep River formation — middle Mio- 



cenic of Montana. 

 Delaware limestone — Niagaran of Iowa, 



also middle Devonic of Ohio. 

 Del Rio formation — upper Comanchic 



(Washitan) of Texas. 

 Delthyrium — in brachiopods, the trian- 

 gular opening under the beak of the 

 pedicle valve, through which in some 

 species the anchoring fleshy pedicle 

 passes (see Fig. 218). 

 Deltidial plates — in the higher brachio- 

 pods (Telotremata), the two plates 

 which grow inward from the sides of 

 the delthyrium and at times com- 

 pletely close the opening. They are 

 secreted by a dorsal extension of the 

 ventral mantle lobe and are never 

 present in the earliest growth stages 

 of the shell (see Fig. 219.) 

 Deltidium — a single triangular plate 

 present in some brachiopods (Protre- 

 mata and some Neotremata), cover- 

 ing the delthyrium. This is secreted 

 by the dorsal surface of the pedicle 

 and since its growth is in an anterior 



direction the growth lines are hori- 

 zontal. It begins to be formed as the 

 prodeltidium, while the animal is still 

 in its embryonic, free-swimming con- 

 dition. 

 Deltoid — shaped like the Greek letter 

 delta A ; wedge-shaped. In crinoids, 

 the interradial plates. 

 Dendroid — branching after the manner 



of a tree. 

 Dental — pertaining to teeth. 



Dental lamellce — same as dental 



plates. 

 Dental plates — in brachiopods, inter- 

 nal plates below the teeth in the 

 pedicle valve (see I., 173). 

 Dental sockets — in brachiopods, the 

 pair of shallow depressions bound- 

 in the beak of the brachial valve 

 internally for the reception of the 

 teeth of the opposite valve (see 

 Fig. 261). 

 Denticles — small teeth or tooth-like 



ridges. 

 Denticulate — toothed. 

 Depressed — on a level with, or below 



the general surface. 

 Des Moinian — lower Coal Measure 



(middle Carbonic) of central U. S. 

 De Soto beds — upper Pliocenic of 



Florida. 

 Dextral — right-handed. The normal 

 direction of coiling in gastropods ; 

 see also sinistral. 

 Di — a prefix meaning twice. 

 Diaphragm — a more or less straight par- 

 tition extending horizontally or diag- 

 onally from one side of a tube to the 

 other (see Fig. 182, d). 

 Dichotomous — regularly dividing by 



pairs. 

 Dicyclic — with two cycles. Applied to 

 crinoids which have infrabasals as 

 well as basals. 

 Diductor — in brachiopods, one of the 

 muscles used in opening the shell 

 (see I., 173; also Fig. 392, a). 

 Digitate — branching like the fingers of 



a hand from a central point, 

 Digonal — two-angled. 



