aaa palaeontology of new york. 



Atr}i)a spinosa, vel. A. aspera. 



PLATE LIII A. 



Atrypa tpinota ; IIali,, Report on Fourth Greological District of New York, p. 200, f. 1 and 2. 



Mrypa dumota : Id. lb. p. 271, f. 1. 



Compare Tertbratulites atpera : Schlothem (Leonhard's Taschcnbiich, pa. 74, tab. 1, f. 7 : 1813 ) ; Nach- 

 tragcn Pctrcfaktenkunde, part 1, p. 863 (95); part ii, 68, tab. 18, f. 3. ALso T. explanata, idem. 



'• Mrypa atpera: Dalmam, Uppst. och Beskrif af de i Sverigc funne Torebrat., Kongl. Vetens. Acad. 



Handlingar, 1827 : pa. 128, tab. iv, fig. 3. 



" T<refrra<u/a(M7>er«: DeFrascb, Diet, liii, p. 164. 1828. 



'• T. reticularis : Beonn in part, Ind. Paloeontologicus, p. 1249. 1848. 



" Mrypa squamota : Sowibbt, Trans. Geol. Soc. Lond., 2d series. Vol. v, pi. Ivii, f. 1. 



" Terebratula (Atrypa) aspera: PHitLiPS, Pal. Fossils of Cornwall, Devon and West Somerset, p. 81, 



pi. xxxiii, f. 114. 1841. 



" Spirigerina reticularit, var. atpera: M'CoT, British Pal. Fossils, p. 879. * 



" Mrypa reticularis, Tar. aspera : Davidson, Monograph of British Devonian Brachiopoda, part vi, 



pa. 57, pi. X, f. 6-8. 



Shell robust, suborbicular or oviod ; width greater or less than the length ; 

 radiatingly costate and concentrically lamellose or spinose ; hinge-line 

 often nearly straight, a little less than the width of the shell. 



Ventral valve depressed-convex, becoming more convex in the upper part ; 

 nearly flat and often a little concave towards the lateral margins, and 

 cardinal extremities depressed or broadly sinuate in front : beak abruptly 

 rounded ; apex truncate and perforate, closely appressed and overlapping 

 the umbo of the opposite valve. 



Dorsal valve convex, becoming gibbous in old shells, flattened or slightly 

 concave towards the cardinal angles, regularly curving to the sides and 

 • baso-lateral margins, and a little elevated in front, but Avithout any dis- 

 tinct mesial fold. 



Surface marked by strong rounded radiating costao bifurcating at unequal 

 intervals, which are much stronger in the middle of the valve, and becme 

 obsolete or appear as gentle undulations towards the cardinal angles. In 

 the middle of the valves there are about seven or eight of these costa3 

 in the space of half an inch. The shell is also marked by strong concen- 

 tric lamellae, which are often about a line apart. In perfect shells these 

 lamell89, at the crossings of the costie, are often produced into tubular 



