102 The Fauna of the Magnesian Series. 



Tryblidium repertum n. sp. 

 PJate V, figures 21 and 22. 



Shell small, low, with the apex towards the posterior and directed 

 backward. Aperture oval, about 11 mm. in longitudinal and 9 mm. in 

 transverse diameter. Apical elevatiou of the shell 6 or 7 mm. From the 

 apex the surface curves gently down to the anterior margin, while on the 

 posterior and along the lateral portions the surface is concave. There are 

 some slight indications of concentric undulations, but other characters are 

 not visible on the casts of oolitic dolomite. 



One specimen referred to this species has a much higher apex and a 

 proportionally narrower aperture supposed to have been caused by Cjbntor- 

 tion previous to its deposition in the stratum, but it is in every respect sym- 

 metrical. 



From the Shakopee dolomite formation near Argyle, Wisconsin. 



Ascoceras gibberosum n. sp. 

 Plate VI, figures 8, 9 and 10, 



All that is known of this species are casts of the septate portion, one 

 of which is sketched. The specimens do not show conclusively that they 

 represent the hollow chambers extending along the chamber of habitation, 

 but presumabl3' that is their nature. The septa, eight or nine in number, 

 are not regularly equidistant, and grow one above and over the other in 

 the dorsal (or ventral) portion of the shell somewhat irregularly but al- 

 ways overlapping the last above and on the sides, but slightly underlap- 

 ping below. This last charncter gives some indication that there may 

 have been also a regular system of septa in the base of the shell. The en- 

 tire shell must have been short and small, with the aperture contracted and 

 oblong ovate dorsoventrally. 



From the Oneota dolomite at Dresbach, Minnesota. 



Cyrtoceras dresbacbense n. sp. 

 Plate VI, figure 4. 



Shell small, expanding somewhat rapidly, and curved. Transverse 

 section ovate, with the apex on the dorsal side. The septa are numerous 

 and arch rather strongly forward on the outer, and also on the inner, sur- 

 face. The siphuncle is small and is situated near the inner side of the shell. 

 The chamber of habitation and the surface of the shell are not known. 

 Septa arched dorso-ventrally, otherwise nearly flat. 



From the Oneota dolamite near Dresbach, Minnesota. 



Cyrtoceras (?) winonicum n. sp. 



Plate VI, figures 2 and 3. 



Shell small, very slowly expanding, straight or slightly curved. The 

 septa ate strongly concave in dorso-ventral direction, very gently so across 



