268 Mr. H. J. Carter on two iindesci'ibed Sponges possibility if it existed ; but it would be much more easy, if the squamosal suture with the parietal bone had become obli-terated, and the specimens studied were few, to suppose that the difficulty could be so explained. The existence of that suture, which is usually well seen, would restore to all the bones of the upper part of the head their usual names ; and in view of the large serpent-like development of the parietals in Ichthyo-saurus, it is not easy to bring one's self to call them squamosals if any other explanation can be given. There would then (excepting also the loss of the supraquadrate bone) be nothing to distinguish the Ichthyosaurus under discussion from other Ichthyosaurs but the anomalous little bones at the back of the nostril, which could neither be nasal nor any named ele-ment of the skull. Than that a new bone should appear in such a place it would seem less improbable that the obscure element should be an accidental dismemberment of an adja-cent bone — probably a part of the lachrymal, which usually extends over the area which the supposed new bone occupies. The lachrymal is often fractured, even in crania which have preserved their natural fonii. Prof. Cope's nomenclature of the bones of the lower jaw does not accord with the structures of any Ichthyosaur known to me. The articular bone is not a long external splint ele-ment, as shown in his figiu'e, but is shaped more like the hoof of an odd-hoofed mammal, and is usually so enclosed in the jaw as only to display its articular surface, and is never seen in a view of the external part of the jaw. There are many points in the Ichthyosauria worthy of attention; and on the relation of the immature to the adult animal I trust soon to be able to offer some new evidence. XXXV. — On two undescrihed Sponges and two Esperiadse from the West Indies ; also on the Nomenclature of the Calci-sponge Clathrina, Gray. By H. J. Carter, F.R.S. &c. [Plate XVII.] In Dr. Bowerbank's ' Monograph of the British Sponges,' published by the Ray Society in 1864, there are two illustra-tions of foreign .sponges without names (viz. figs. 289 & 292, vol. i.), the former of which is stated to be " West Indian," and the locality of the other is not mentioned. For these two sponges Dr. Gray, in his " Notes on the Ar-rangement of Sponges " generally, has proposed the names of Ectyon sparsus and Acarnus innominatus respectively (Proc. Zool. Soc. 1867, pp. 515 & 544).
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