462 Prof. P. M. Duncan and Mr. W. P. Sladen on 



to warrant its removal, in our opinion, from that species, even 

 as a provisional variety. 



In some cases great irregularity is exhibited in the mouth- 

 papillse, one abnormal example being particularly worthy of 

 notice. In the OpMoglyphce the innermost mouth-papilla 

 generally" stands immediately over the teeth, and might be 

 easily mistaken for a tooth, being, in fact, affixed to the tooth- 

 plate and not to the lateral plates. In 0. Sarsii, as well as 

 in other members of the genus, two additional papilla? are 

 generally associated with it, one on either hand, and are in 

 like manner borne by the ossicle upon which the teeth are 

 placed. 



In consequence of this arrangement it has long seemed 

 probable to one of us that these subdental papillae should be 

 regarded as tooth-papillae (of which they are in truth the 

 homologues) rather than as mouth-papillae, so-called, along 

 with which they are commonly counted. One of the speci- 

 mens taken in Discovery Bay throws considerable light upon 

 this question. 



In this individual the dental armature consists of four teeth 

 regularly superposed, following upon which, and occupying the 

 same breadth as a tooth, are three ossicles, which fit to one 

 another wedgewise with sloping 

 sides. Then come two which fit 

 together and correspond in their 

 shape with the irregularities of 

 the upper and under tier, which 

 latter consists of from three to five 

 compact close-fitting papillae ; and 

 these again are succeeded by 

 three or four (in some rays five) 

 moderately long, round -tipped, 

 smaller papillae, the whole form- 

 ing a compact mass suggestive, 

 in the highest degree, of ordi- 

 nary tooth-papilla, such as occur, 

 for instance, in OpMothrix ; and 

 yet in every detail, even to mea- 

 surements, the specimen con- 

 forms to the diagnosis of OpMo- 

 glyplia Sarsii. This individual 

 has a disk-diameter of 22 millims. 



Bearing in mind the tendency towards vertical reduplication 

 of the mouth-papillae in some genera, this cannot fail to be 

 regarded as suggestive of the manner in which primitive tooth- 

 papillae may have been developed ; nor is such an assumption 



1^%"^ 



Abnormal development of the 

 dental armature in O. Sarsii. 



