362 THE PALEONTOLOGY OF MINNESOTA. 



LSrlii/.aml>Oll(y> lockil. 



along the posterior margin do not pass over nor around the pedicle, but stops on 

 each side; therefore during this period, there is an open pedicle slit, which is after- 

 wards closed posteriorly by the addition of shell matter underneath the pedicle. 

 As the pedicle opening advanced, the shell was resorbed anteriorly, and a deposit 

 formed posteriorly, as indicated by the strong convex lines in the pedicle furrow. 



Schizambon ? dodgii differs from S. ? fissus, var. canadensis Ami*, in being smaller, 

 more broadly oval, in having a dorsal sinus, and the spines shorter, thicker, and 

 therefore less numerous. If Siphonotreta ? minnesotensis Hall should prove to belong 

 to Schizambon, it will still be found to differ from S. ? dodgii in the much thicker 

 spines and the many large openings in the shell on the posterior portion of the 

 dorsal valve. 



Formation and locality. Two specimens and fragments of others were collected by Mr. W. W. 

 Dodge, of Cambridge, Massachusetts, for whom the species is named, in a dark, compact limestone near 

 the top of the Trenton at Sandy Hill, New York. Associated fossils are Trematis terminalis Emmons, 

 and Trinuoleus concentricus Eaton. The types were kindly presented to one of the writers. 



SCHIZAMBON (?) LOCKII, n. sp. 



PLATE XXX, PIGS. 8-10. 



Shell large, very thin and broadly oval in outline. Dorsal valve shallow, not 

 as deep as the ventral, and evenly convex laterally and anteriorly. Surfaces shining, 

 nearly smooth, marked by fine, concentric growth lines and delicate, radiating striae. 

 At the apex the former are Paterina-shaped, but after this stage growth takes place 

 more strongly anteriorly than laterally, which soon gives to the shell its specific 

 form. At about two-thirds the length of the shell from the beak to the anterior 

 margin, the fine, radiating striae have numerous, very small, elongate, but distinct 

 pustules, which probably did not terminate in spines. 



Ventral valve most elevated at the beak, with gradual slopes laterally and 

 anteriorly, and abrupt ones posteriorly. Apex obtuse, situated at about one-sixth 

 the length of the shell from the posterior margin, with the pedicle furrow originating 

 at the highest point, and gradually widening and extending forward not quite to the 

 center of the valve in the smaller specimens; while in the larger it terminates at 

 one-third the length of the shell from the posterior margin. Surface marked by 

 concentric, slightly elevated growth lines, a number of which continue around 

 posterior to the apex, and gradually become more distant and prominent as growth 

 progresses. On each side of the pedicle furrow are a few radiating striae, while in 

 front of the former the concentric growth lines have numerous, very small but dis- 

 tinct tubercles, about ten in 3 mm., which are probably the bases of former spines. 



Ottawa Naturalist, Dec. 1H87; see also Pal. N. Y., vol. rill, p. 1. p. 115, pi. 4, figs. 32-36, 1892. 



