17 o NORTH AMERICAN INDEX FOSSILS. 



walls generally thick, with numerous thin spines projecting in- 

 ward from them. 



Choptank and Calvert formation of Maryland. 



175. M. rimulata Ulrich. (Fig. 217, h.) Eocenic. 

 Zocecia hexagonal, arranged quincuncially with longitudinal 



rows generally regular ; apertures occupying entire cell, quite reg- 

 ularly ovate in form ; interapertural space narrowed and rounded, 

 sometimes angular, often with depressed central line. 

 Aquia formation of Maryland. 



CVI. Adeonellopsis Macgillivray. 



Encrusting with bulbous cells having subcircular to semicircular 

 opening, beneath which is a second circular or crescentic pore. 

 Cret.-Tert. 



176. A. umbilicata (Lonsdale). (Fig. 217, i.) Miocenic. 

 Irregular nodose masses of numerous layers; zocecia irregular, 



central and anterior portion elevated and outline of each marked 

 by a row of pores; upper front wall coarsely punctate; orifice 

 anterior, semielliptical, 2 smaller apertures on the proximal portion 

 of the cell. 



Chesapeake Group of Virginia and Choptank formation of Mary- 

 land. Common. 



CVII. Schizoporella Hincks. 



Zoaria variable ; zocecia urn-shaped, the front entirely calcified ; 

 orifice varying from semicircular to suborbicular, with a distinct 

 notch or sinus in the lower margin. Cret.-Recent. 



177. S. informata (Lonsdale). (Fig. 217,7.) Miocenic. 

 Irregular botryoidal or nodulose masses of superposed layers of 



zocecia, 20 to 40 mm. in diameter ; cells with terminal subcircular 

 orifice with distinct peristome and deep and sharp proximal notch ; 

 entire surface punctate ; avicularia uncommon. 



Chesapeake group of Virginia and Choptank formation of 

 Maryland. 



Class Brachiopoda. 



Brachiopods are marine animals secreting a shell of two pieces 

 or valves which may be calcareous or phosphatic or both. These 

 valves are dorsal and ventral in position and are usually of unequal 

 size, a larger, the pedicle or ventral valve and a smaller, the brachial 





