CAMBRIAN BRACHIOPODA. 329 



Family PATERINID^ Scliiicliert. 



Geniis MICKWITZIA Schmidt.a 



Miekwitzia ScHiiroT, 1888, M^m. Acad. imp. sci. St.-Petersbourg, 7th ser., vol. 36, No. 2, p. 24, (Described in German 

 as a new genus.) 



Miekwitzia Schmidt, Hall and Clarke, 1892, Eleventh Ann. Kept. State Geologist New York for 1891, p. 246. (De- 

 scribed.) 



Miekwitzia Schmidt, Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum for 1891, p. 562. (Copy 

 of preceding reference.) 



Miekwitzia Schmidt, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 86-87. (Described 

 and discussed.) 



Causea Wiman, 1902, Bull. Geol. Inst. Univ. Upsala, vol. 6, pt. 1, No. 11, pp. 53-54. (Described and discussed in 

 German as a new genus, the description being incorporated with that of the type species, Causea formosa.) 



Miekwitzia Schmidt, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 143. (Classifica- 

 tion of genus.) 



Shell large, unequivalve. Ovate or subcircular, with apex of valves within the margin 

 and erect, or curved over the margin. A false cardinal area may or may not be obscurely defined; 

 valves not articulated. Shell substance mostly calcium phosphate and arranged in three prin- 

 cipal layers. The outer layer is papillose, with fine and large punctae; middle layer marked 

 by numerous radiating and concentric, more or less elevated lines and small punctse that become 

 very numerous toward the front margins of the shell; inner layer marked by large punctse or 

 vertical canals and often a thickening of shell substance that takes the form of irregular ser- 

 pentine ridges penetrated by vertical canals. 



Type. — Lingula f raonilifera Linnarsson. 



Observations.— Both Schmidt [1888, p. 24] and Hall and Clarke [1892c, pp. 86-87] define 

 and discuss this genus, but with the new material I have for study, a new diagnosis has been 

 prepared. The genus appears to fall within the order Atremata Beecher [1891, p. 354] and 

 the family Paterinidse Schuchert [1897, p. 119]. The latter family has heretofore included 

 only the genus Micromitra. The species of Mickmtzia include chitinous or phosphatic shells 

 with elevated ventral valve, having an apex elevated witliin the margin {Miekwitzia forTnosa 

 (Wiman)), or arching over the margin (Miekwitzia monilifera (Linnarsson)). Mieromitra has a 

 clearly marked area and pseudodeltidium, in this resjject being further advanced in evolution 

 than Miekwitzia. A series of shells of Miekwitzia might show a more strongly marked false 

 area in the young shell than in the adult forms. 



The generic name was given in honor of Dr. A. Mickwitz. 



MiCKwiTziA FORMOSA (Wiman). 

 Plate VI, figures 3, 3a-c. 



Causea formosa Wiman, 1902, Bull. Geol. Inst. Univ. Upsala, vol. 6, pt. 1, No. 11, pp. 53-54, PI. II, figs. 1-5. (De- 

 scribed and discussed in German as a new species. The specimen represented by figs. 1-5 is redrawn in this 

 monograph, PI. VI, figs. 3, 3a-c.) 



OutUne of ventral valve circular; apex a little in front of the posterior margin, strongly 

 elevated, and rising vertically above a broad, obscurely defined false area. The area is defined 

 by a rounded angle where the transverse, sUghtly convex posterior surface below the apex 

 unites with the lateral slopes from the apex. The posterior margin is sHghtly arched, so as 

 to form an opening between it and the dorsal valve. 



Only the inner layers of the shell are preserved on the type specimen, the outer epidermal 

 layer having been exfohated. On the posterior portion of the shell the second or middle layer 

 has the radiating and concentric fines typical of Miekwitzia monilifera (Linnarsson). Toward 

 the front the layer of shell is marked by faint radiating lines and many fine punctae, exactly 

 as in specimens of M. monilifera, where the outer layer is exfohated. This type of surface is 



a Prior t^ the definition of Miekwitzia by Schmidt [18SS, p. 24], the species now referred to this genus were placed under the following genera: 

 Linmla Linnarsson [1869a, p. 344; 1869b, p. 398]. Obolus Linnarsson [1871, pp. 9-10]. 



