32 GILBERT C. BOURNE. 



There is a pair of ciliated post-ocular tentacles on either side 

 of the head (I find vestiges of these structures in the adult of 

 F. gra^ca), a well-developed pair of ciliated epipodial ten- 

 tacles in the vicinity of the opercular lobe, and a corneous 

 raultispiral operculum. Even the gills, if one may judge from 

 Boutan's figure (PI. xlii, fig. 8), have a close resemblance to 

 those of a Scissurellid. If the animal were sexually mature one 

 would not hesitate to place it among the Scissurellidae, In the 

 next or Kiinuliform stage the epipodial tentacles are multi- 

 plied ; Boutan figures six in addition to the sub-ocular tentacles 

 in F. reticulata and two in F. gibba. The labral incision 

 has been converted into a foramen by the approximation of its 

 edo-es at the labrum, but a suture still connects the foramen 

 with the margin of the shell. This condition is exactly paral- 

 leled by the vScissurellid genus Schismope. Subsequent de- 

 velopment leads to the assumption of Fissurellid characters. 

 The visceral spire, and with it the spiral coils of the shell, become 

 obsolete. The foramen in shell and mantle become situated 

 at the summit of the Patelliform shell, the post-ocular and 

 epipodial tentacles (which obviously belong to the same 

 series) degenerate, the operculum is cast off, and the oper- 

 cular lobe disappears. In short, the Fissurellid develops 

 alono- lines which remove it further and further from the 

 Scissurellid condition of the larva. 



But, as must be apparent from the preceding pages, there 

 is a considerable number of anatomical features in which the 

 adult Scissurellid more nearly resembles the adult Fissurellid 

 than any other family of the Ehipidoglossa. These features 

 may be shortly recapitulated, Incisura being taken as a type 

 of Scissurellid structure. 



The jaws of Incisura in position and structure very closely 

 resemble those of a Fissurella. The radula of Incisura 

 lytteltonensis finds its nearest counterpart in the radula 

 of Subemarginula picta, and in general is distinctly 

 Fissurellid in character. In the alimentary tract the characters 

 of the salivary glands and oesophageal pouches, the absence 

 of a spiral caecum in the stomach, the presence of an oeso- 



