INVERTEBRATE PALAEONTOLOGY. 169 



Cardinm (Criocardium) speciosum, M. & H 

 Plate 37, 6gs. 4, o, 6, c 



( ardium speciosum, Meek and Harden (Nov., 1S5<>), Proceed. Acad. Nat. Sci. Pliilad., VII 1, 274. 

 Cardium (Acanthocardia) speciosum, Meek (1H04), Smithsonian Check-L'st Cret. Fossils, 12. 



Shell broad-ovate or subcircular, usually higher than long, very gibbous 

 in the central and umbonal regions; anal margin slightly less rounded than the 

 other; base regularly rounded; border crenulate? ; beaks much elevated in 

 old shells, but more depressed in smaller specimens, very slightly oblique, 

 pointed, incurved, and almost exactly central : surface ornamented by num- 

 erous very regular, simple, radiating costae, apparently about as wide as the 

 grooves between, in each of which latter, on the more convex part of the 

 valves, there is a series of small tubercles, very regularly arranged. 



Length, 0.57 inch ; height, 0.67 inch ; breadth, 0.48 inch. 



The surface-markings are not very well preserved in our specimens ot 

 this species, and consequently present some variety of appearances in their 

 various conditions of weathering, even on different parts of the same indi- 

 vidual. Sometimes the costae appear as though broader than the grooves 

 between ; while in other conditions they seem to be about of the same 

 breadth, or even narrower. Where the surface is much weathered, the 

 costae are often so deeply exfoliated as to leave the intermediate spaces stand- 

 ing out in relief, so as to present the appearance of having the tubercles 

 arranged on the ribs instead of between them. 



The tubercles do not exist on the anterior and posterior portions of 

 valves, but occupy the grooves only on the more convex'central region. None 

 of our specimens are in a condition to show whether or not these tubercles 

 were ever so prominent as to form short spines. On the interior, they seem 

 to have been each represented by a corresponding pit, or depression, which 

 leaves a distinctly elevated point on the cast. Where the exterior is exfoliated 

 so as to leave but a thin lamina of the shell adhering to the cast, these little 

 elevations are seen perforating' it with such remarkable regularity, as to 

 present the appearance and arrangement of the fenestrules in some of the 

 delicate reticulate Po/i/zoa; this is the usual appearance of the surface of 

 weathered specimens. In a few cases, where the surface is in a better state 

 of preservation, traces of fine concentric strige are visible, curving strongly 

 upward in crossing the ribs. 

 22 h " 



