1 49 



or with tubercles or spines. Living 

 species (marine) commonly adhering to 

 algae. 



Spirorbis angulatus. Hall. ( Fig. 

 30.) (15th Rep't X. Y. State Mas. Nat. 

 Hist., p. 84.) 



Distinguishing Characters. — Two or 

 more volutions, outer one robust ; sub- 

 angular sides: upper angular surface 

 sometimes nodose; aperture round or fig.30. spirvrbu anguto- 



in i t .i tits. Attached to ;i sliell of 



oval, usually nearly rectangular to the Athyris spin/eroides. Nat- 



, . . ural size and enlarged. 



plane OI VOllltlOn. (Original.) 



Found in the Demissa bed, and occasionally in the shales 

 below, at Sections 5 to 8, and on the Lake Shore (rather rare). 



Genus ADTODETUS. Lindstrom. 



(1884: On the Silurian Gastropoda and Pteropoda of Gotland, p. 185.) 



Tube a sinistral (left-handed) coil, somewhat resembling 

 a gastropod shell. The form is that of a truncated cone, 

 whose exterior is smooth, seldom showing any traces of the 

 internal coil, though covered with a fine nndulose and some- 

 times rugose concentric striation. The apical extremity is 

 flattened into a broad cicatrix of attachment, which some- 

 times has one-half the width of the body-whorl. Usually 

 attached to a brachiopod shell. Walls of the tube thick, 

 somewhat cellular in the thickest portions. 



A U T O I) E T D S LINDSTRCEMI. 



Clarke. (Fig. 31.) 



(Am. GeoL, Vol. XIII., p. 334, 

 Figs. 1,2, 3, May, 1894.) 



Distinguishing Characters. — 

 Rapid expansion of shell; cica- 

 trix of attachment less than one- 

 third the diameter of the body- 

 whorl. Found in the Hamilton 



shales, at Hamburgh, X. Y. Fig. 31. Autodetus lindstroemi. 



. Lateral anil top view, and section. 



(Clarke. ) x 3 (after Clarke;. 



