306 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXV. 



Genus TETRADELLA Ulrich. 



Tetradeila Ulbich, Jour. Cincinnati Sm-. Nat. Hist., XIII, 1890, pp. 112- 



114. 

 Tetradeila Miller, North Amor. Cool, and Pal., First App., 1892, p. 711. 

 Tetradeila Ulbich, Geol. and Nat. Hist. Surv. Minnesota. Final Rept., III. 



Pt. 2. 1894, i». 077. 

 Beyrichia (part) of Authors. 



Based on Tetradeila quadrilirata, the genotype, and drawn up so 

 as to include the subjoined list of unquestioned species, this genns 

 may be characterized as follows : 



Carapace small, 1 mm. to 2 mm. long, eqnivalvecl, never tumid, 

 somewhat oblong, varying from snbqnadrate to snbovate, with the 

 hinge line straight. Valves depressed-convex, deeply trisnlcate, the 

 furrows separating four more or less sharply elevated ridges. As a 

 rule the ridges connect ventrally, but are quite distinct at their 

 dorsal extremities, the result being a semielliptical submarginal ridge 

 with two simple or double, equal or unequal, and less curved ridges 

 within the inclosed space. These inner ridges commonly unite with 

 the ventral part of the marginal ridge and extend upward from it 

 toward the dorsal edge, the posterior one often failing to reach it. 

 Free margins usually with a simple flattened border, which in certain 

 cases extends beyond and conceals thickened contact edges. Surface 

 of valves usually smooth, occasionally minutely granose. 



All of the species of Tetradeila and of the new subgenus Kieso- 

 wia, a list of which follows, are derived from Ordovician strata. 

 FIST OF SPECIES OF TETRADELLA. 



Tetradeila ? affinis (Beyrichia affinis Jones). 



Tetradeila bohemica (Beyrichia bohemica Barrande MSS. Jones). 



Tetradeila bussacensis (Beyrichia bussacensis Jones). 



Tetradeila ciiriuttta (Beyrichia carinata Krause). 



Tetradeila complicata (Beyrichia complicata Salter). 



Tetradeila complicata decorata (Beyrichia complicata, var. decorata 

 Jones). 



Tetradeila V digitata Krause (Beyrichia digitata Krause). 



Tetradeila ? digitata separata (Beyrichia digitata, var. separata steus- 

 loff). 



Tetradeila (Kiesowia) dissecta (Beyrichia dissecta Krause). 



Tetradeila ? erratica (Beyrichia erratica Krause). 



Tetradeila harpa (Beyricha harpa Krause). 



Tetradeila 1 lacunata (Beyrichia lacunata Jones and Holl). 



Tetradeila lunatifcra (Strepula lunatifera Ulrieh). 



Tetradeila (Kiesowia) mamillosa (Beyriohia mamillosa Krause). 



Tetradeila marchica (Beyrichia marchica Krause). 



Tetradeila marchica angustata (Beyrichia marchica, var. angustati 



Krai i so i . 



Tetradeila marchica lata (Beyrichia marchica, var. lulu Krause). 

 Tetradeila palmata (Beyrichia palmata Krause). 



" American species. 



