Lozver Silurian Fauna of Minnesota. 329 



Ventral valve provided with a tube which opens from the apex towards 

 the posterior margin. This species corresponds in many respects to D. 

 pelopea Billings, but his description and figure lejive some doubts which 

 prevent me from labeling my specimens D. pelopea Billings 



This shell is wrinkled, as shown by concentric grooves on casts of the 

 interior, and these could not possibly erode away. Also the color is uni- 

 versally white, in strong contrast to the dark shells of an associated crania. 

 And there may be some other differences. I have not a specimen of D. 

 pelopea with which to compare. 



From the Lingulasma bed, Berne and Mantorville, Dodge county, and 

 the Blue (2d) bed at Minneapolis. 



LEPTAENA MINNESOTENSIS U. Sp. 



Plate IV, figures 24 and 25, 



Compare JL. sericea Sowerby. 



Shell small, length of largest specimen seen 8 mm., breadth 13 mm. 

 on the hinge line, which is the greatest exfension of the shell. Dorsal 

 valve concave following the convexity of the ventral valve. Surface 

 marked by fine radiae as in case of L. sericea Sowerby. No concentric 

 lines. The specimens figured are the largest out of two hundred from 

 ten localities in Ramsey, Goodhue and Fillmore counties. In general ap- 

 pearance and even in internal structure these agree closely with L. sericea 

 Sowerby. I have a number of the last named, from the Stictopora and 

 Fucoid beds in Minnesota, and they agree in every particular with the 

 first figures of L. sericea in Paleontology of New York, Vol. i. With 

 these L. minnesotensis may easily be confused unless attention be paid 

 to a few particulars. Specimens of L. minnesotensis are uniformly smaller 

 have no concentric lines (?), are more strongly curved. That they are 

 not immature forms is shown by the thick shell and heavy visceral area, 

 thicker and heavier if anything than in the mature forms of L. sdricea 

 Sowerby. L. sericea (as identified in Minnesota) and L. minnesotensis 

 are never associated in the same strata so far as known. The former 

 stops in the fucoid bed while the latter appears in the Zygospira bed, and 

 continues up into the Camarella bed. There are some small differences 

 of detail on the interior markings. 



Common in the Zygospira bed and throughout to the Camarella bed, 

 where exposed in Minnesota. 



LEPTAENA PRAECOSIS n. Sp. 



Plate IV, figures 26, 27 and 28. 



Compare L. transversalis Sowerby. 



Shell small, very convex, length 9 mm. or less; breadth nearly twice 

 that, hinge line as long as possible. Area on the convex valve very large 

 with a triangular deltidium. No concentric lines. Interior not known. 



This species agrees closely with L. transversalis Sowerby, but never 

 attains the large size figured in the Palaeontology of New York. The 

 form of the shell is quite invariable. 



Common in the Maquoketa shales of the Cincinnati group, wherevtr 

 exposed in Fillmore county, Minn. 



