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Updated: June 11, 2025
Some of them have no solid covering; but the greater part are protected by a single shell, and on this account they are called Univalves, in contradistinction to the Acephala or Bivalves. These shells, though always single, differ from each other by an endless variety of form and color, from the flat simple shell of the Limpet to the elaborate spiral and brilliant hues of the Cones and Cowries.
Not only have the invertebrata, as shown by geological data, altered at a less rapid rate than the vertebrata, but if we take one of the classes of the former, as for example the mollusca, we find those of more simple structure to have varied at a slower rate than those of a higher and more complex organisation; the Brachiopoda, for example, more slowly than the lamellibranchiate bivalves, while the latter have been more persistent than the univalves, whether gasteropoda or cephalopoda.
Surely this is a poet that has got an inkling, in some way, of the new idea of an experimental philosophy, of a combination of the human faculties of sense and reason in some organum; one, too, whose eye passes lightly over the architectonic gifts of univalves and bivalves, and entomological developments of skill and forethought, intent on that great chrysalis, which has never been able to publish yet its Creator's glory.
Here I picked up four varieties of shells two univalves and two bivalves all very interesting from being quite unknown in the conchological world. There were numbers of them lying on the pebbly beach. 7th. We started at dawn as usual; but again at sunrise, the wind increasing, we put in for the shore, for these little cranky boats can stand no sea whatever.
As to the univalves, I have seen from a pit of Red Crag, near Woodbridge, a large individual of the extinct Voluta Lamberti, seven inches in length, of which the lip, then perfect, had in former stages of its growth been frequently broken, and as often repaired.
The hard parts of the many animals which live upon the reef become imbedded in this coral limestone, so that a block may be full of shells of bivalves and univalves, or of sea urchins; and even sometimes encloses the eggs of turtles in a state of petrification.
The shelly strata, also, have occasionally suffered denudation, and the removed portions have been replaced by clay." Out of 224 species of univalves obtained from the Minchinhampton beds, Mr. Lycett found no less than 50 to be carnivorous.
The univalves dredged among the Louisiade Islands in this region of depth were mostly known forms, such as Conus betulinus, Oliva sanguinolenta, Mitra exasperata, Terebra maculata, consors and labiata; these were all taken in less than six fathoms water. The bivalves of this region were but few.
Among the fossil shells common to Madeira and Porto Santo, large cones, strombs, and cowries are conspicuous among the univalves, and Cardium, Spondylus, and Lithodomus among the lamellibranchiate bivalves, and among the Echinoderms the large Clypeaster called C. altus, an extinct European Miocene fossil. The largest list of fossils has been published by Mr.
It is now admitted that about one-third of these Miocene forms, univalves and bivalves included, agree specifically with living mollusca, so that much more than the enormous interval which divides the Miocene from the Recent period must be taken into our account when we speculate on the origin by transmutation of the shells now living, and the disappearance by extinction of intermediate varieties and species.
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