CAEDIUM (PROTOCARDIA) JUDAICUM. 51 



The three examples of this species are two entire shells retaining the test 

 complete, and a single right valve. In the smaller entire one the surface at 

 the posterior umbonal slope is so remarkably preserved that the minute 

 spinules which stud the radial ribs are in part retained, and witli the delicate 

 lamellae which cross the ribs are conspicuous vmder the lens. In some of the 

 spaces between the ribs the lamellae have all their original sharpness and 

 perfection. Of the same specimen, shown in figs. 5 h, c, the beaks have been 

 pressed into actual contact, while in the normal example, of which a right 

 side view is given in fig. 5 a, they are separated by a small space. 



Lartet (op. cit., p. 130, PI. xi, fig. 5, and PI. xii, fig. 9) figures, without 

 description, under the name CardUmi Ililhumm Sow., var. Mouhiiicum, a shell 

 which, as figured, agrees essentially with immature individuals of the typical 

 Ilillumim from the Blackdown Hills of Devonshire. The three specimens 

 upon which the present species is based are obviously distinct from HiUanmn. 

 Comparison with a full series of the species last named from the Blackdown 

 Greensand, and with many casts of the same from Lebanon, shows the fol- 

 lowing differences. In the side view, the outline of Ilillanum is rotundate- 

 cordate ; of this, subquadrangular. The concentric markings of the former 

 are numerous stria? with very small intervening ridges ; of the latter, wide 

 and flattish varices, separated by well impressed furrows. Tlio posterior 

 iTmbonal slope of Hillamnn is always flattened, while that of the species 

 in hand is somewhat concave, and near the posterior margin is suddenly 

 compressed, the compressed part including a straight and very gently de- 

 .scending hinge line. 



Nor is this species C. hifrouH Reuss (Kreideschichten in den Ostalpen, 

 p. 145, PI. xxviii, fig. 19, 1854), which is a variety of Ilillanum. Our fossils 

 most nearly resemble C. Vatloni Coquand (Geol. et Paleont. de Constantine, 

 p. 207, PI. xi, fig. 5), which is readily distinguishable by having tubercles 

 upon its twenty posterior radiating ribs. 



LocnlUi/ and Position. — The single valve, from the Merrill collection, was 

 taken from ferruginous and arenaceous marl, and therefore cannot be refer- 

 able to the Cardium zone of the Turonian, which is made up of brown lime- 

 stone and contains only casts of various species of Cardiiun. The entu'e 

 specimens, from the Bird collection, ai'e apparently from the same kind of 

 rock, which seems to be identical with the arenaceous marl of the Gastero- 

 pod zone, already noticed. As, according to Fraas, that zone yields fairly 

 preserved specimens of C. Ilillanum, it is not improbable that this species is 

 from the same horizon. 



