86 PALEONTOLOGY OF NEW YORK. 



Genus MICKWITZIA, Schmidt. 1888. 



1888. MicJcioitzia, Schmidt. Ueber eine neuendeckte untei'oambrische Fauna in Estlanrt ; Mem. de 



I'acad. imp. des Sciences de St. Pelersbourg, vii Ser., tonne xxxvi, No. 

 2, 11. 24. 



Diagnosis. Shells large, thick, unequivalve. Dorsal valve flat, circular ; 

 ventral valve oval, convex, produced ^^ ^_ 



into an acute apex, beneath which lies ^0" \ /^^^^k.- / 



a triangular, more or less distinctly ^^ ; / ' J 



developed cardinal area. Valves ^^i^p^^'^ 'X ■ - v^ 



not (?) articulated. Shell-substance ma^^ monmf.ru. 



composed of thin coarsely punctate jiier3cuMiL.T. 



^ •' ^ Fig. 4'3. Peilicle-valve. Fig. 4J. Interior of same valve. 



layers alternating with prismatic i^'g. 44. E.^terior of brachial vaive. 



laminse which are traversed by scattered vertical canals. Surface covered with 

 radiating stride. Shell composed of calcic phosphate. 

 Type, M. monilifera, Linnarsson. 



This name has been proposed by Dr. Schmidt for a shell which had been 

 described by Linnarsson in 1869,* from the Eophyton sandstone, the oldest 

 fossil-bearing formation of Sweden, and referred at that time to the genus 

 LiNGULA (?), ; subsequently by the same author in 1871,1 to Obolus (?). More 

 a,bundant material found near Reval has shown various features which have led 

 to its establishment as a separate genus. The shell has the general appearance 

 of Obolus, and its relationship to this genus is shown in the external charac- 

 ters, and the grooved cardinal area. Unfortunately none of Dr. Schmidt's 

 specimens give a satisfactory indication of the internal characters, so that the 

 generic value of the species must still remain in great doubt. A remarkable 

 feature is shown in a single figure of the interior of the smaller valve, viz , a 

 single large tooth-like process, situated centrally behind the beak, and bent at 

 a sharp angle backward into what would have been the umbonal region of the 

 opposite valve.^ Dr. Schmidt is not convinced that this is to be regarded as a 



* OtVer. af K. Vetensk. Akad. Forhandl. p. 344, t. vii, figs. 1, 2. 



t Kong-1. Svenska Vetensk. Akad. handlingar, Bnd. 9, No. 7, p. 9, pi. i, figs. 2, 3. 



I Schmidt, pi. ii, fig. 16. 



