Conus loomisi (Dall & Ochsner, 1928)

Description:

Shell of moderate size, solid, with a slightly concave, acute spire, and about 12 whorls exclusive of the (lost) nucleus; suture distinct, whorls between the sutures excavated, marked only with concavely retractive inceremental lines, corresponding to a sulcus at the aperture; shoulder well marked but rounded; body in front of the shoulder with slightly convex sides, constricted somewhat behind the canal ; sculpture of the posterior half of the body obsolete, consisting of very narrow incised lines with much wider flat interspaces; on the anterior half of the body these lines gradually become wider excavated channels, numbering about eight on the canal, which in the adult has a marked siphonal fasciole, there being three or four more grooves; aperture narrow, wider anteriorly; canal deep, wide, very slightly recurved⁽¹⁾.

Height, 44 mm. ; height of last whorl, 38 mm. ; diameter at shoulder, 22 mm.

Holotype: No. 2910; paratypes: Nos. 2911, 2912, Mus. Calif. Acad. Sci., collected by W. H. Ochsner, March 5, 1906. 1 ¼ miles northeast of Vilamil, Albemarle Island, Galapagos Group. Probably Pleistocene⁽¹⁾.

The recent shell which most nearly approaches this is Conus lucidus, which occupies the same region at present. This is a shorter and more stumpy shell with less conspicuous sculpture⁽¹⁾.

The species is named for Mr. Leverett Mills Loomis who was Director of the Museum of the California Academy of Sciences at the time the Galapagos Expedition was organized⁽¹⁾.

The fauna of the Galapagos Islands has been the subject of much discussion. The islands have been held by some to have been a part of the American continent, separated by subsidence of a connecting area; others have considered them to be a permanently isolated group formed by volcanic action and built from the depths of the ocean by volcanic ejections. Still another hypothesis is that they form the remnants of an outlying archipelago of a former Pacific continent now submerged below the sea.
A discussion of the recent fauna by eminent specialists has led to the conclusion that in large part it is of American derivation, modified by long isolation. This is especially true of the land animals, while the marine invertebrates, although predominantly of American affinities, also include a small proportion of forms now more characteristic of the Pacific islands to the westward and southward. However, the marine invertebrate fauna of Clarion Island, one of the nearest to the Galapagos, so far as yet explored, is of a strictly Indo-Pacific type and presents a strong contrast to the fauna of the Galapagos⁽¹⁾.

One of the most interesting and important of the discoveries made by the Academy's Expedition of 1905-1906 was the discovery of fossil Mollusca in several places.

Formerly it was supposed that the islands were wholly of volcanic origin, or at least destitute of fossil-bearing sedimentary rocks. The discovery of these not only affords a clue to the minimum age of the Galapagos group, but also an indication of the sources from which its fauna has been derived. It is known that about the end of the Oligocene period, or in the early Miocene, a movement in elevation of the earth's crust in the Panamic region resulted in the union of the continents of North and South America and the closing of the gap between them through which the Eocene marine fauna of the north and west shores of South America had previously extended.

It seems a reasonable hypothesis that, during the widespread volcanic activity of the Miocene, the Galapagos group, or its preexisting nucleus, underwent enlargement and elevation, a process which the discoveries made by the Academy's expedition show continued, perhaps intermittently, into Pleistocene time⁽¹⁾.

The characteristics of the fossils collected are, with hardly an exception, typically American. The faunas are tropical, as might be expected, but there is nothing of a typical Indo-Pacific nature, although some of the species belong to groups widely distributed in tropical seas, both of America and elsewhere⁽¹⁾.

While most of the species belong to groups now represented in the Panamic fauna there are a few which recall forms now existing only on the Antillean side, and quite a number which belong rather to the subdivision of the Panamic fauna now existing in the Gulf of California, than to the warmer waters of the Gulf of Panama. The inference might be drawn from this that at the time the Galapagos fossil forms were living, the temperature of the local seas was somewhat cooler than at present⁽¹⁾.