374 THE PALEONTOLOGY OF MINNESOTA 
{[Crania trentonensis. 
CRANIA TRENTONENSIS Hall. 
PLATE XXIX, FIGS. 36 and 37. 
1866. Crania trentonensis HALL. Description of new species of Crinvidea and other Fossils, p. 12. 
1872. Crania trentonensis HALL. Twenty-fourth Rep. N. Y. State Cab. Nat. Hist., p. 219. pl. vu, 
1892. Crania trentonensis bss taster aes of New York, vol. viii, pt. i, pl. rvH, figs. 21, 22. 
Original description: “Shell medium size, strongly convex on the upper valve; 
width a little greater than the length, greatest width below the middle of the shell. 
Beak of dorsal valve small, pointed towards and situated near the cardinal border. 
“Surface marked by strong concentric lines of growth. No striz or radiating 
lines are visible. Transverse diameter eleven-twentieths of an inch; length half an 
inch.” 
This species differs from C. setigera Hall, in not having the upper or dorsal valve 
covered with elongate pustules. The shell of the dorsal valve of C. trentonensis is 
thick, and in this differs from C. scabiosa Hall, which is thin and usually partakes of 
the ornamentation of its host. Outline of the shell and position of the apex are 
variable features, and of little specific value among species of Crania. 
Formation and locality—In Minnesota this species has been found only in the Galena shales near 
Cannon Falls. One of the writers has found it in the ‘‘ Lower Blue beds” of the Trenton at Janesville, 
Wisconsin, and Dixon, Illinois. The type specimens are from the Trenton at Middleville, New York. 
Collectors.—W. H. Scofield and C. Schuchert. 
Mus. Reg. No. 7697. 
Genus CRANIELLA, @blert. 
1888. Craniella, GAHLERT. Bull. dela Soc d’ Etudes Scientif. d’ Angers, p. 37. 
1892. Craniella. HALL. Paleontology of New York, vol. viii, pt. i, p. 153. 
Description: “Shell somewhat irregular, outline subcircular or subquadrangular. 
Ventral valve thin, adhering by its entire surface; dorsal valve conoidal, more or less 
elevated; apex subcentral, posterior; interior of the dorsal valve without a well- 
defined border; impressions of the adductors large, very distinct, four in number, of 
which the posterior two are quite distant, the two subcentrals somewhat smaller, 
closely approximate or even confluent; from near each of the posterior impressions 
starts a vascular sinus, which is broad, strongly sinuous near its point of departure, 
narrowing gradually in following the contour of the valve, emitting from its mar- 
ginal side dichotomizing secondary branches, 
“Type:  Craniella meduanensis @hlert.” (Hall’s translation of the original 
diagnosis.) 
The known species of this genus are C. ulricht Hall of the Trenton, C. hamil- 
tonie Hall of the Hamilton, and C. meduanensis blert of the Devonian of France. 
