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Show 1878.] MR. CHEESEMAN ON NEW OPISTHOBRANCHIATES. 275 present, being in one case nearly as large as the constant first premolar, while in another it is a mere rudiment ; in the other four examples it is altogether absent. In the number of the functionless teeth of the lower jaw (which I carelessly called small incisors in my previous paper, but which Professor Owen regards as the homo-logues of the canines and anterior premolars ') there is the greatest possible variety, one example having three in one ramus and none at all in the other; three, however, appears to be the normal number. These differences have nothing to do with the age of the individual ; for the extra upper premolar is absent in a half-grown animal, and the small lower teeth are present in one of evidently great age. It appears, therefore, that the dentition of this genus is even more variable than has been believed, and that the existence of the additional teeth must be dropped from the specific characters of C. orientalis. I may add that in several of these specimens, which are all females, the dark dorsal stripe is absent; this also has been regarded as a diagnostic character. 7. Descriptions of three new Species of Opisthobranchiate Mollusca from N e w Zealand. By S. T. C H E E S E M A N , F.L.S., Curator of the Auckland M u s e u m. [Eeceived January 29, 1878.] (Plate XV.) From a number of new species of Opisthobranchiate Mollusca collected in or near Auckland Harbour I have selected for description the three following prominent forms. 1. PLEUROBRANCHUS ORNATUS, n. sp. (Plate XV. figs. 1, 2.) Bodv 3-4 inches long, broadly elliptical, depressed, nearly equally rounded at both ends, colour varying from pale buff to a clear reddish brown, with irregularly disposed blotches of a rich dark red-brown; mantle large, extending over and concealing both head and foot, quite smooth, margin thin, entire ; dorsal tentacles short, stout, abruptly truncate, finely transversely wrinkled, approximate at their origin, but gradually diverging at their apices; colour reddish brown tipped with white ; eye-specks black, placed a little distance behind the tentacles, embedded in the integument, but appearing through it; oral tentacles united in front by a thin semicircular expansion which forms a veil concealing the mouth, and which is carried in advance of the foot; mouth roundish, with fleshy lips ; buccal plates two, regularly reticulated ; odontophore with numerous rows of similar unciform teeth. Branchial plume placed in the groove between the foot and the mantle, very large, 1 Odontograpby, i. p. 382. 18* |
