108 PROCEEDINGS OF THE ACADEMY OF [1884. 



With the German specimens of the Maerkische Rupelthon and 

 the Sternberger Oligocene, two specimens from Ashley, S. C, 

 one from the upper strata of Claiborne (which are apparently 

 Oligocene), and one specimen of typical Pleurot. cristata Conr. 

 from Vicksbnrg were compared. The latter was obtained for 

 comparison through the kindness of Professor Heilprin of Phila- 

 delphia. 



Both German and American forms vary in slenderness ; Coch- 

 lespira engonata Conr. is apparently one of the shorter speci- 

 mens. In the Ameiican forms the number and sculpture of the 

 revolving lines seem to be generally more developed, but these 

 vary too. Conrad says : " Cochlesp. bella differs from G. cristata 

 in having fewer and coarser lines and a more prominent carina." 



What Edwards figures as Pleur. Volgeri Phil, looks quite 

 different. Much more like seems to be his PL terehralis Lam., 

 of which he describes six varieties. The opinions of the German 

 authors as to the identity of P. Volgeri Phila. and P. terehralis 

 Lam. are varying. I am greatly inclined toward uniting them, 

 but for want of sufficient material prefer withholding a positive 

 opinion on this point. 



4. Saxicava arctica L. 



1766. Mya arctica L. 



Linn., Syst. Nat. ed. 13, p. 1113. 

 1836. Saxicava arctica L. 



Philippi, Enum. Mollusc. Sicil., etc., i, p. 20j tab. 3, fig. 3. 

 1838. Saxicava biUneata Conr. 



Conrad, Medial Tertiary or Miocene fossils of the U. Si, p. 18, tab. 10, 

 flg. 4. 

 1844. Saxicava arctica L, 



Nyst., Coq. foss. Belg., p/ 95, tab. 3, fig. 15 a-c. 



1846. Saxicava arctica L. 



Loven, Ind. moll. Scand., p. 40. 



1848. Saxicava arctica L. 



S. V. Wood, Crag. Moll., ii, p. 287, tab, 29, fig. 4 a, b. 

 1856. Saxicava arctica L. 



Hoernes, Wiener Becken, p. 24, tab. 3, fig. 1, 3, 4. 

 ? 1860. Saxicava Jeurensis Desh. 



Deshayes, Anim. s. verteb., i, p. 170, tab. 10, fig. 18, 19, 20. 

 1863. Saxicava bicristata Sandb. 



Sandberger, Concbyl. d. Mainzer Beckens, p. 277, tab. 21, fig. 6. 



