562 Forty-fifth Report on the State Museum. 



tated under a lens of moderate power, except by the ends of 

 these fibers. 



Type, Spondylobolus craniolaris, McCoy. Lower Silurian 

 (Llandeilo). 



Mickwitzia. Schmidt. 1888. 



Shells large, thick, inequivalve. Brachial valve fiat, circular ; 

 pedicle-valve oval, convex, produced into an acute apex, beneath 

 which lies a triangular, more or less distinctly developed cardinal 

 area. Valves not (?) articulated. Shell-substance composed of 



. Mickwitzia monilifera. (After Schmidt ) 

 Fig. 253.— Pedicle-valve. Fig. 254.— Interior of same Fig. 255.— Exterior of 



valve. brachial valve. 



thin, coarsely punctate layers alternating with prismatic laminae 

 which are traversed by scattered vertical canals. Surface 

 covered with radiating striae. Shell composed of calcic phosphate. 

 Type, M. monilifera, Linnarsson. Lower Cambrian. 



Schizobolus, Ulrich. 1886. 

 (Plate 3, Figs. 16-19.) 



Shell oval, slightly inequivalved ; cardinal margins somewhat 

 thickened. Shell substance largely corneous ; external surface 

 concentrically lined. In the pedicle-valve, the passage is very 

 short,. Usually no more than a notch on the margin. From its 

 inner end a median ridge extends one-third the distance across 

 the valve, and this is flanked on each side by a low muscular 

 callosity. Narrow curved lateral scars extend from the post- 

 lateral margins of this callosity, continuing to. or beyond the 

 center of the valve. In the brachial valve is a narrow thickened 

 hand directly within, and parallel to the posterior margin. 

 Muscular thickening as in the opposite valve. No curved lateral 

 scars. 



Type, Schizobolus t/nmoatoiS) Hall (sp.). Devonian. 



A single species has been desoribed; from the Genesee shales. 



114 



