BRACHIOPODA. 



371 



Schlzocranla fllosa.] 



beak, and extending nearly or quite one-fourth of the length of the valve from the 

 apex. There are also two other muscular impressions [anterior adductor scars] 

 smaller in size, circular in form, and situated near the middle of the valve below 

 the extremities of the ovate imprints, and slightly more distant from each other. 

 Beneath the beak there is a slight thickening of the cardinal border. The muscular 

 markings of the lower valve have not been observed. 



"Surface of the shell of the convex valve [dorsal] marked by fine, even, thread- 

 like radiating striae; increased both by division and implantation, and gradually 

 increasing in strength toward the border of the shell; the interspaces where the 

 shell is perfectly preserved are flattened, the striae appearing as raised lines on the 

 surface. The attached valve [ventral] is strongly marked by irregular concentric 

 undulations circling the valve parallel to the margin, but interrupted at the border 

 of the notch." 



When the dorsal valve is broken away so as to show the ventral valve beneath, 

 it is seen that the first overlaps and completely surrounds the latter, and it may, as 

 believed by Hall, (op. cit. 1892, p. 143), have served as "an important accessory means 

 of attachment" to foreign bodies. This species is usually found attached to brachio- 

 pods, particularly to Rafinesquina alternata, but is occasionally found on gastropods, 

 as in the case of the Minnesota specimens before us. 



a 



FIG. 31. a, three immature specimens attached to Strophomena, natural size; 6, two of the 

 same x 7; c, same x 18. Middle third of the Trenton shales, Minneapolis. Collection of C. Schuchert. 



These figures are introduced to show various stages of the nepionic and early 

 nealogic condition of Schizocrania. The "Paterina stage," with its straight hinge- 

 line, continues throughout the nepionic growth and is succeeded in the early nealo- 

 gic stage by the development of series of radially arranged pits strongly resembling 

 those of Trematis. This is followed by the striated or specific stage. Schizocrania, 

 therefore, seems to be phylogentically related to Trematis. 



Formation and locality. In the Trenton shales at Cannon Falls, Chatfleld and Minneapolis, 

 Minnesota. This species also occurs in the Trenton formation of New York and Kentucky; in the Utica 

 formation at Utica, New York, and Ottawa, Canada; and in the Utica horizon at Cincinnati, Ohoi. 



Collectors. W. H. Scofleld, E. O. Ulrich and C. Schuchert. 



