..] 



.tl form tin i- nut known to o.vut in the Trenton, hut a variety has 



been found in the < 'litainbonites bed of the Trenton group '" Minnesota. For this 

 we propose the >ul>ordinaU> name iin pecimens being unusually small, none 



exceeding 11 mm. in diameter. The volutions seem also to he narrow, the hight at 

 the aperture in the specimens at hand exceeding the width by about one-sixth. The 

 surface markings are precisely as in the typical form of the species excepting that 

 the trans\erM' -tru- in crossing the dorsal carina are sometimes bent slightly 

 backward. The variety is of consequence chieHy because it proves the existence of 

 the orw//n.v type at nuite as early a time as that in which the C. retrorsus lived. 

 Anil tli , unities us also in denying that C. ornatus was evolved from C. 



Formation and locality. The typical form In a common fossil of the Lormioe and Richmond groups 

 at numerous localities InOhlo, Indiana, Kentucky. IVrmsylvaiila, New York and Canada. At Cincinnati 

 the 1< n covered by a parultlc bryozoan ( Leptotrypa ornata Ul rich) which, when carf ully chipped 



way, generally leaves a good cast of the surface markings and not Infrequently the test Itself. The 

 species has not yet been certainly Identified In tin- I'Ura group, ),ut we suspect that one or two casts 



;.-.! in the lower part of this group at Oovlngton, Kenim-ky. may IH-II.IIK t< It. Variety minor was 

 i. O. Ulrlch In tli.- Clltambonltes bed of the Trenton group, near Cannon Falls, Minnesota. 



On RETRORHU8, n. -;-. 



I-I.ATI: i. MI. no*. -w. 



11 rather small, the diameter rarely exceeding 15 mm., in one case 20 mm., 

 in others mostly from 12 to 14 mm.; in general appearance decidedly like C. ornatus, 

 the dorsal slopes being strongly undulated, and the surface distinctly reticulated. 

 Carefully compared, however, it is found to differ in the following particulars: the 

 keel is more prominent, the dorsal slopes are more concave, the sides sharper, the 

 transverse section of the volutions more distinctly quadrangular, and their rate of 

 increase greater. The most important difference is in the form of the mouth and 

 the direction of the transverse surface lines. The mouth namely is deeply cut out 

 ami the lines instead of passing directly across the back are strongly curved back- 

 ward. Finally there is a small ridge along the suture line that has not been 

 observed in C. < The retral curve of the transverse lines is slightly greater 



than in C. e-irinnhis Miller, with the typical form of which C. retrortus agrees very 

 closely so far as the inner volutions are concerned. But mature specimens of the 

 two species cannot be confounded, the dorsal slopes in Miller's species becoming 

 Hat with maturity, while undulations are not developed except in the oldest 

 examples. In C. retrorsus, on the contrary, they begin very early, while the con- 

 cavity of the dorsal slopes continues through all stages. 



There can be no reasonable question about the specific distinctness of this shell, 

 nor do we doubt that it will include, if not all, at least a part of the Tennessee 



