Maryland Geological Survky 539 



Genus CRATERELLINA n. gen. 



This genus is erected for a small group of early Devonian Ostracoda, 

 two of which are illustrated in this work. One of these is found in great 

 numhers upon the surface of dark siliceous shales of Lower Oriskany age 

 at 21st Bridge. Although the preservation of this material is not of the 

 best, still a sutticiently large number of individuals were found to indicate 

 that the original of pi. xcviii, fig. 21. is a normal example, and that its 

 surface characters are as indicated. The second forni is a larger but less 

 abundant species in the same formation. Both species occur in com- 

 parative abundance in the Lower Oriskany cherts at Cash Valley, Mary- 

 land, and other forms are known in rocks of similar and earlier age 

 elsewhere. 



The most obvious characteristic of the genus is the presence of a crater- 

 like depression bordered by a more or less distinctly elevated rim occupy- 

 ing the anterior third or half of each valve. Otherwise the general shape 

 and relation of the valves, and other characteristics, ally the new genus 

 Craterellina to Thlipsura and Octonaria. However, the absence of the 

 posterior sulci of the former and the proportionally great size of the single 

 large round excavation in the anterior part of the valve impart a suffi- 

 ciently peculiar aspect to the five or six species which it is proposed to 

 refer here to justify their generic separation from all established genera. 



Type CratereMina rohusta n. sp. 



Craterellina robusta n. sp. 

 Plate XCVIII, Fig. 21 



Description. — Valves rather broadly subovate, the ventral edge con- 

 siderably less curved than the dorsal, and the posterior end much narrower 

 than the anterior. The crater-like depression in the anterior half extends 

 practically to the edge of the valve. An extension or projection into the 

 depression from the posterior side of the surrounding rim tends to divide 

 the cavity into two more or less equal halves, each of which is marked by 

 a node-like prominence. A rather distinct rim borders the posterior half. 

 Remainder of surface broadly convex, and exhibiting occasional puncta?. 



Length of right valve 1.25 mm.; height 0.9 mm. 



