BRA OHIO POD A. 373 



Crania granulosa.] 



the Treuton shales often attain a greater size, and have the setae usually less pro- 

 nounced, while the beak is obtuse, the outline variable, and the cardinal margin 

 only in rare instances straight. Free dorsal or upper valves are common, and but 

 few specimens have been secured in which the valves conjoin, and are attached to 

 an Orthis or Bafinesquina. These attached specimens are marked more or less with 

 their host, causing the characteristic surface pustules to become obsolete, while 

 the striae of those growing upon smooth surfaces have developed the setae. In 

 specimens where these pustules have been removed by weathering or other causes, 

 it is very difficult to decide whether they are individuals of C. setigera or C. trenton- 

 ensis. Such specimens are usually referred to the latter species, but they commonly 

 preserve a few pustules near the margin. 



A specimen of Monticulipora, with an individual of this species* attached, also 

 has a parasitic species of bryozoan growing on it, which grew towards the Crania. 

 Its growth, however, was limited towards the anterior portion of the Crania, leaving 

 between it and the encroaching bryozoan a space 3-4 mm. in width. This limiting 

 of the growth of the bryozoan may have been caused by the frequent extension of 

 the arms of the Crania during life. 



Formation and locality. In the Trenton limestone at Minneapolis; Trenton shales at Minneapolis, 

 St. Paul, Cannon Falls, Fountain, Ohatfleld and Preston, Minnesota. Also from the Trenton at Decorah, 

 Iowa; Mineral Point and Beloit, Wisconsin. In the Salmon River group or Lorame shales at Wilmington, 

 Illinois. 



Collectors. C. L. Herrick, W. H. Scofleld and the writers. 

 Mus. Reg. Nos. 718, 5500, 7692-7696, 7958, 



CRANIA GRANULOSA N. H. Winchell. 



PLATE XXIX. FIGS. 34 and 35. 



1880. Crania granulosa N. H. WINCHELL. Eighth Annual Rep. Geol. and Nat. Hist. Survey of 



Minnesota, p. 63. 



Original description: "Shell small, but prominently elevated at the beak; orbi- 

 cular or somewhat widened between the antero-lateral margins; no concentric striae 

 or undulations visible on the exterior of the shell, nor radiations; the whole surface 

 of the dorsal valve uniformly fine-granulated or pustulose; these granulations not 

 disposed in any apparent order. The lower valve unknown." 



Crania scabiosa Hall, when growing on a bryozoan, usually has the upper valve 

 strongly pitted. Specimens of this nature have received the name C. multipunctata 

 Miller and Dyer. The outer surface of C. granulosa, however, is not pitted, but is 

 crowded with small pustules irregularly arranged. 



Formation and locality. Trenton limestone at Minneapolis, Minnesota. 

 Mus. Beg. No. 708. 

 *This specimen is figured in Pal.. N. Y., vol. viii, pi. ivH, fig. 14, 1892. 



