PALEONTOLOGY. 463 



-valve regularly and evenly convex, and marked only by very fine concentric lines 

 of growth. 



In the interior of the shell the median line is marked by an elevated 

 ridge, representing muscular scars, which reaches fully two-thirds the 

 length of the valve. The impression contains four elements, two above 

 and two below, the upper pair inclosing the upper half of the lower. 

 Near the rostral extremity another widely diverging pair of scars are 

 seen, which also appear double. 



The specimen is undistinguishable from examples of L. (D.) ligea 

 Hall, from New York, where it occurs in the Hamilton and Portage 

 groups. The median line of muscular scars and the diverging rostal 

 scars show that it belongs to the section of L,ingulidse for which Prof. 

 Hall proposed the generic name Dignomia. 



Formation and Locality. — In the calcareous nodules from the Huron 

 shales at Delaware, and also from the Erie shales, at Leroy, Lake 

 county, Ohio, with Echinocaris, etc. 



Plumulites Newberryi. 

 Plate VIII, figs. 6-11. 

 Plumulites Newberryi, Whitf., Ann. N. Y. Acad. Sci., 1882, p. 217. 



The specimens for which the above specific name is proposed, con- 

 sist of several detached plates, and of one of several plates, irregularly 

 folded together in such a manner as to be difficult of interpretation 

 The several plates vary considerably in form among themselves, and. 

 probably represent those from different parts of the body. 



The general form of the plates is triangular, with the apex, or initial point 

 of growth, a little inclined to one side; the base, or margin of accretion, is usually 

 the longest side, but not in all cases. One set of plates has the shorter side s 

 diverging at nearly right angles. On this form, the basal line is convex for more 

 than two-thirds its length, and concave on the remaining portion, giving a 

 sigmoidal outline ; of the shorter sides, one is straight to near the apex, where it 

 becomes rounded, and the other is slightly concave. Another form has the shorter 

 sides diverging at kn angle of about 105 degrees, one slightly convex and the other 

 concave ; while the basal margin is convex in two sections, with a constriction or 

 interruption between the two sections, or at about one-third of its length from the 

 straight margin. The plates of this and the preceding form have the surface reg- 

 ularly annulated transversely, parallel to the basal . margin, the annulations very 

 fine, and regularly increasing in size and strength from the apex to the base, ex- 

 cept in aged specimens, where they are again crowded near the border: five un- 

 dulations may be counted in an eighth of an inch where strongest. These forms, 

 also, have the straight margin often fractured and bent, as if they had been broken 

 along that side ; indicating that two such plates may have been united along this 

 line; and on the only individual showing several plates together, this would ap- 

 pear to be the case. A third form of plate is narrowly triangular or conical, the 

 basal border being the shortest, and simply convex ; the other sides being slightly 

 curved thoroughout, but more distinctly so near the apex, which is obtusely 

 rounded ; the lateral margins are of unequal length, and the annulations of the 

 surface finer arid more closely arranged than on the other forms. 



