Obs.—This species, considered by Mr. Gabb as of probably miocene age, is closely allied to the _S. striatula_, which is found living on the Californian coast, and occurs fossil in the _faluns_ (miocene formation) of Bordeaux, France; but it differs from it in the outlines and the size of the shell, the former being comparatively small and longer than broad, while the latter is broader than long. Besides, the apex of the _S. Gibbsii_ is situated more posteriorly, and the lateral petals, in the _S. striatula_, diverge from the apex, with an angle of from one hundred and ten to one hundred and fifteen degrees; this latter has also its ambulacral furrows more ramified at their extremities. _S. interlineata_ W. P. Blake. Disk sub-circular, broad, upper surface convex towards the middle, depressed on the margins, plane beneath; apex central; ambulacral star symmetrical; petals long, equal, closed at their extremities, nearly reaching from the apex to the margin of the shell, terminated by five or six irregular hexagonal plates. The petals are longitudinally divided into four rows, which are connected by numerous and regular transverse lines of pores. Mouth central; anus submarginal; ambulacral furrows symmetrical, not much ramified. Inter-ambulacral areas occupied by two rows of pentagonal plates, convex, of equal length, increasing in size until they unite with the ambulacral plates; hexagonal from that point and decreasing towards the margin. Two sorts of appendages; spinous processes numerous and crowded, above and beneath. Spines of the superior surface short, striated, pyriform, irregularly pentagonal or hexagonal; inferior spines slender, comparatively long, dentaliform, striated longitudinally, tubular and round. Obs.—Water-worn fragments of this fine fossil occur in abundance on the beach, between Merced Lake and the Pacific, south of Point Lobos, in San Francisco County. It was made known to science by Mr. W. P. Blake, Geologist of the Railroad Survey, who found it in 1853, among the shingles thrown up by the surf, and first described by Mr. W. Stimpson. At that time the locality whence the scutellæ were derived had not been discovered, so that the specimens obtained being imperfect, no complete description could be made; this is the reason why I offer a new and complete description of the _Scutella interlineata_, from specimens procured _in situ_. As was suggested by Mr. W. P. Blake, the rocks bearing these fossils are found a few miles southward, north of the boundary line between San Mateo and San Francisco Counties, where the scutellæ stick out from conglomeratic sandstones, which Mr. Gabb considers as belonging to the _pliocene_ or _post-pliocene_ formation; we find them in a fine state of preservation, with their spines retained.