„ , LAMELLIBEANCHIATA. 559 



vanuxemia aubrotunda.] 



Hist. Sur. Minn., p. 239.) On comparison it proved to haVe a thinner shell, to be more 

 erect and more rounded in outline, also more ventrieose and with a stronger umbonal 

 ridge, while there are only two cardinal teeth instead of three or more. A fourth 

 form I propose soon to describe, in one of the periodicals, under the name of 

 V. gihbosa. It is from the lower Trenton of central Kentucky, and differs from 

 the present species in being more gibbous, in having larger umbones, almost 

 terminal beaks and" more obtuse anterior side. A fifth is associated with the 

 preceding in Kentucky, and also occurs in Tennessee. It is a Very thick shell and 

 attains to larger size than V. hayniana, from which it differs further in its form 

 which is, higher and straighter and more obtuse in front. But the principal differ- 

 ence lies in the ligamental area which is at least twice as high as in adult examples 

 of Safford's -species. The area is shown in four specimens and in all of them its hight 

 is 4 mm. or more at the middle and in one it is quite 5 mm. For this form I propose 

 the name Vanuxemia cardinata. Finally a sixth form of this type is known to me 

 from about twenty very perfect specimens that I owe to the liberality of Prof. J. M. 

 Safford. He collected them at "Haynies," the locality in Smith county, Tennessee 

 from which he obtained also the types of his "Cyrtodonta hayniana." For the present 

 I shall arrange these specimens as a small variety of V. gibhosa, since they agree 

 much better with that species than with true V. hayniana. 



Formation and locality.— 11x6 types of this species are from the TrentOQ limestone (middle Nashville 

 beds of Safford) in Smith county, Tennessee. In Kentucky the species occupies two narrow horizons 

 separated by more than 100 feet of strata. The first is at the base of the Trenton limestone in Mercer 

 county at a point about three miles south of High Bridge, where the decomposed limestone has left 

 numerous silicifled shells and cystidrans. ,The second horizon, which is near the top of the Trenton, 

 is exposed at several points along the Cincinnati Southern railroad between Burgin and Danville. In 

 Minnesota the species seems to be restricted to the Galena shales, in which it occurs as casts of the 

 interior at several localities in Goo'dhue county and at Bt. Paul. Good specimens are rare. 



Vanuxemia subeotunda n. sp. 



PLATE XXXVIII, FIGS. 36-38. 



This species differ from V. hayniana Safford sp., to which it is doubtless very 

 closely allied, in its more uniformly rounded outline, broader anterior end and 

 shorter hinge line, and. in having the beaks smaller and situated farther behind the 

 anterior extremity. The convexity of the valves also is less, and the shell is thin- 

 ner, particularly in the umbonal and anterior parts where the internal thickening 

 is so little that no perceptible sulcus nor ridge is left in casts of the interior. For 

 the same reason the beaks on casts must be more rounded and larger, so that how- 

 ever much trhe exterior of the two shells may resemble each other, casts of the 

 interior would be distinguished very readily. V. nana Ulrich, from the upper Trenton 

 in Kentucky, is a smaller shell; with more ventrieose valves, better defined umbonal 



