No. 136.] 91 



Geological formation and locality. In strata of "the age of the Hudson- 

 river group; in Kentucky. Received from David Christy, Esq., of Cin- 

 cinnati. 



I have under consideration several species of Orthis from the 

 shales of the Hudson-river group, which have been placed in my 

 hands by Mr. Carly of Cincinnati. Two of these are of the 

 type of 0. occidentalis and 0. sinuata^ etc. ; and since the entire 

 characters and degree of variation of these forms have not been 

 fully determined, I hesitate to designate other species until I 

 have a larger collection for comparison. I take this occasion, 

 however, to say to those palaeontologists who have regarded the 

 three species of this type described in Vol. I, Pal. N. Y., as one 

 species, and identical with 0. porcata of Europe, that in my col- 

 lections may be found specimens of the type which can only be 

 referred to three distinct species ; for the illustration of which, 

 I hope to procure the separated valves to show the interior 

 markings. In the mean time, I shall feel under obligations to 

 any persons who can aid me in obtaining other specimens for the 

 more' satisfactory determination of this question. 



CYCLONEMA VENTRICOSA ( n. s.). 



Shell turbinate ; height and greatest breadth about equal. 

 Spire consisting of about four volutions, which increase rapidly 

 -. in size, the last one extremely ventricose ; the lower side some- 

 what flattened near the upper ^ part of the columella, which is 

 straight and thickened. Aperture as wide as high, transversely 

 semioval. 



Surface marked by strong revolving strige, about three of which 

 on the upper volutions, and four or more on the last volution, 

 become more strongly developed, and give a subcarinate form 

 to the volutions ; between these, the striae are fewer and 

 unequal. The revolving striae are crossed by finer lines of 

 growth, which on the upper volutions are nearly uniform, but 

 towards the aperture become crowded, unequal and sublamel- 

 lose. 



This species resembles the Pleurotomaria ( Cyclonema) percarinata of 

 the Trenton limestone, but is more ventricose, with different surface 



