NORTH AMERICAN INDEX FOSSILS, 



square or rectangle and one in the 

 middle. 

 Quinnimont formation — middle Pots- 

 ville (lower Carbonic) of Appalach- 



Rachis — the central stem of the frond, 

 in Bryozoa, etc. 



Racine beds — lower Siluric (Niagaran) 

 of Wisconsin, etc. 



Radials — the five main plates of the 

 calyx of a crinoid, resting on the 

 basals and alternating with them ; 

 they are the lowest of the plates form- 

 ing an unbroken line from the arms 

 (see Figs. 1864, 1907, R). For use 

 in echinoids, see ocular plates. 



Radianal — in crinoids, the second anal 

 plate (see II., 491). 



Radicular — root-like. 



Radii — ribs or striations diverging 

 from the beak of a shell. 



Radula — in gastropods and cephalopods, 

 the file-like lingual ribbon used in 

 boring into shells and for tearing up 

 food. 



Raisin River dolomite — lower Monroan 

 of Michigan, Ohio, etc. 



Raleigh formation — division of the 

 Potsville, Virginia. 



Ramifying — branching. 



Ramose — branched. 



Ramus — branch of a skeletal structure. 



Rancocas formation — upper Cretacic of 

 Atlantic coast. 



Raritan formation — upper Comanchic 

 of Atlantic coast. 



Ray — in crinoids, one of the arms or 

 arm trunks. 



Reading qiiartzite — lower Cambric of 

 Pennsylvania. 



Rectangular — right-angled. 



Red Bank sands — middle Cretacic 

 (Monmouth) of Atlantic coast. 



Red Wall limestone — Mississippic of 

 Grand Canyon. 



Regan sandstone — middle Cambric of 

 Oklahoma. 



Regular — applied to an echinoid with 

 mouth at center of bottom of test and 

 anus at center of top ; endocyclic (see 



Fig. 1920). 



Reniform — kidney-shaped. 



Resilifer — the spoon-like shelly struc- 

 ture projecting from the hinge plate 

 in some pelecypods (as Mactra) for 

 the reception of the resilium ; the 

 chondrophore. 



Resilium — the internal cartilage or 

 compressible substance in the hinge 

 of pelecypods. 



Respiration — the act of breathing ; the 

 aggregate of those processes by which 

 oxygen is introduced into the system 

 and carbon dioxid is removed. 



Resupinate — inverted in position. In 

 brachiopods, applied to those shells 

 with the brachial valve convex and 

 the pedicle valve concave (ex. Stro- 

 phomena). 



Reticulate — resembling a net-work. 



Retractile — capable of being with- 

 drawn. 



Retral — back ; posterior. 



Retrosiphonate — see siphonal funnel. 



Retroversal — backward bending. 



Rhabdosome — the colony of graptolites 

 derived by budding from a single 

 polyp. 



Rhaetic — upper division of the Tri- 

 assic. 



Rhomboid — an oblique-angled parallel- 

 ogram with only opposite sides equal. 

 A rhomb has all four sides equal. 



Rhomb oidal — having the outline of a 

 rhomboid. 



Rhynchonelloid — resembling Rhyncho- 

 nella. 



Ribs — the radial or transverse folds 

 upon shells. In brachiopods and 

 pelecypods they are radial ; in cepha- 

 lopods they are transverse. 



Richmond group — upper division of the 

 Cincinnati group. 



Rico formation — upper Carbonic of Col- 

 orado. 



Riley series — upper(?) Cambric of 

 Texas. 



Ripleyan — middle Cretacic of the At- 

 lantic coast. 



Rochester shale — division of the Niag- 

 aran of New York. 



