Lozuer Silurian Fauna of Minnesota. 335 



closely related. The ventral valve is sometimes a little more convex 

 near the centre like 6^. camerata Conrad. In some points it strongly 

 resembles 6". ponderosa from the top of the hills at Cincinnati, O., and 

 I am inclined to look upon it as closer allied to that form than to S. 

 alternata Conrad of the Trenton formation. 



The specimen figured is from the Stictopora bed, at Saint Paul, 

 Minn., but the species probably occurs in higher beds also. 



STREPTORHYNCHUS SUBSULCATUM n. Sp. 



Plate IV, figure 39. 



Compare S. sulcatum Verneul. 



Shell semicircular, length of a large specimen 12 mm., breadth 15 

 mm. Both valves gently convex. Mature specimens have a short 

 sinus on the ventral valve, a fold on the dorsal and usually a rounding 

 ■out of the anterior margin. Interior unknown. 



Compared with 5^. sulcatum Verneul, as figured by Mr. Meek; the 

 only differences noted are a narrower area, shorter sinus, greater length 

 and finer radiate markings and more equally convex valves. The rela- 

 tion of this form to 6*. sulcatum and 6". sinuatum, in view of Mr. Meek's 

 observations on the two last mentioned species, (Pal. Ohio, Vol. i, p. 

 88) is interesting, since the coarser plicated species occur at an eleva- 

 tion intermediate between the other two. 



From the Orthisina bed, Saint Paul, and in Goodhue county. 



ZYGOSPIRA AQUILA n. Sp. 



Plate IV, figures 15, 16, 17 and 18. 



Shell small; length (of a large specimen) 6 mm.; breadth a little 

 less; depth 3 mm. Ventral valve convex, with a broad median ridge; 

 beak sharp, long, curved in continuation of the convexity of the 

 valve, and perforated. Dorsal valve more evenly convex, shorter and 

 more circular. Surface smooth and brown in color. Plications several, 

 extending part way to the beak. The outward appearance led me to 

 think this a Camarella, but sections show an internal process similar 

 so far as I have been able to observe, to that of Zygospira modesta. A 

 thick section of the ventral valve cutting the beak of the dorsal valve 

 is figured to indicate the position of the process. From other sections 

 there appear to be spiral coils anterior to the part shown in the figure, 

 situated in the dorsal valve mainly, and with the apices together. 



Found in the Buff limestone at Minneapolis; also about the same 

 horizon in Olmsted and Fillmore counties. 



CARINAROPSIS DELETA n. Sp. 



Plate VI, figures 5 and 6. 



Shell small, consists of one or two coils in the same plane, very 

 rapidly enlarging so that the last half coil constitutes nearly the whole 

 shell. Aperture elliptical, entire. Surface (on casts) concentrically 

 marked, but not clearly. The minute coil is seldom preserved and the 

 general form is then that of a metoptoma, but without a subtruncated 



