300 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxv. 



Beyrichia having been developed from diverse stocks by convergence 

 in evolution, is worth bearing in mind. In general aspect, and es- 

 pecially in having a well-defined median pit, B. granulifera and B. 

 v-scripta certainly indicate Primitian ancestry, close affiliations being 

 suggested to both Primitia and Eurychilina (as, for instance, E. 

 schmidti). However, an analysis of their lobes seems to show more 

 positive alliances on the one hand to the B. clavata group of Bey- 

 richia, and on the other to the proposed subgenus Steusloffia. Per- 

 haps it would be well to institute another subgenus for this group. 



Genus KLCEDENIA Jones and Holl. 



Kloedenia Jones and Holl, Ann. ami Mag. Nat. Hist. (5), XVII, issc, 



!». 362. 

 Klccdenia (part) Krause, Zeits. d. d. geol. CJessell., XLI, 1889, p. 21. 

 Kloedenia (part) Miller, North Amer. Geol. and Pal., First App., 1892, 



p. 70S. 

 Kloedenia (part) Koken, Die Leitfossilien, 1896, p. 39, text fig. 26A. 

 Beyrichia (part) of Authors. 



Carapace of moderate size, 1 mm. to 4 or 5 mm. in depth. Valves 

 very nearly equal, the ventral edge of the right valve sometimes very 

 slightly overlapping the edge of the left. Outline oblong, sub- 

 quadrate to subovate, rarely subtriangular, the hinge line long and 

 straight, the remaining sides more or less curved. Surface of valves 

 strongly convex, especially in the unlobed ventral half; dorsal half 

 with two furrows deep above but growing obsolete before or shortly 

 after crossing half the valve. Anterior furrow deeper and broader 

 than the posterior one and located near the mid-length. Of the three 

 lobes the median is the most constant in size and form. It is gen- 

 erally rounded and somewhat bulbous, more rarely obtusely pointed 

 above, and its diameter usually about one-fifth of the length of the 

 valve. Posterior and anterior lobes sharply defined only along the 

 furrows, the outer parts usually sloping more or less gently to tin' 

 end rims and below merging into the swollen ventral surface, their 

 dorsal extremities occasionally projecting beyond the horizon line. 

 Posterior lobe varying in width from rather less than to nearly twice 

 the diameter of the median lobe. Anterior lobe constituting the 

 greater part of this half of the valve, sometimes divided so as to form 

 a broad inner lobe and one or two narrower ridges in front. When 

 the anterior lobe is thus prolonged and divided (as. for instance. K. 

 plicata Jones), the separating furrows extend entirely across the 

 valve. Ventral pouch (as in Beyrichia presumably of female) mostly 

 posterior, merely an extra, obscurely outlined swelling, not globular 

 as in Beyrichia. A simple, narrow, flange-like border commonly 

 present but may be wanting. Surface of valves granulose, punctate, 

 reticulate, or without ornament. 



