1878.] MR. CHEESKMAN ON NEW OMSTHOBRANCHIATES. 275 



present, being in one case nearly as large as the constant first pre- 

 molar while in another it is a mere rudiment; in the other four 

 examples it is altogether absent. In the number of the functionless 

 teeth or the lower jaw (which I carelessly called small incisors in 

 my previous paper, but which Professor Owen regards as the homo- 

 logies 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 num- 

 bei. Ihese differences have nothing to do with the age of the in- 

 dividual ; 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. J 



It appears, therefore, that the dentition of this genus is even more 

 variable than has been believed, and that the existence of the addi- 

 tional eeth must be dropped from the specific characters of C. 

 orientals. I may add that in several of these specimens, which are 

 all females, the dark dorsal stripe is absent; this also has been re- 

 garded as a diagnostic character. 



7. Descriptions of three new Species of Opisthobranchiate 

 Mollusca from New Zealand. By S. T. Ciieeseman, 

 I.L.S., Curator of the Auckland Museum. 



[Received January 29, 1878.] 



(Plate XV.) 



From a number of new species of Opisthobranchiate Mollusca 

 collected in or near Auckland Harbour I have selected for descrip- 

 tion the three following prominent forms. 



1. Pleurobranchus ornatus, n. sp. (Plate XV. fiVs. 1, 2.) 

 Body 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, 

 s out abruptly truncate, finely transversely wrinkled, approximate 

 at heir 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 semi- 

 circular expansion which forms a veil concealing the mouth and 

 which is carried in advance of the foot; mouth roundish,' with 

 Hesny h ps . 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 Odontography, i. p, 382. 



18* 



