30 GILBERT C. BOUKNE. 



on the anterior face of the foot in the groove between it and 

 the lower surface of the snout. The posterior pedal glands 

 are a mass of unicellular glands lying above the epithelial 

 cells of the sole of the whole posterior surface of the foot. 

 Each unicellular gland has its own duct, which runs between 

 the epitlielisd cells to open on the surface. 



The genera Scissurella, Schizoti-ochus, Incisura and Schis- 

 inope, which have been grouped as a separate family Scissu- 

 rellidee by some few authors, are generally placed in the family 

 Pleurotomariidse because they are zygobranchiate Eliipido- 

 glossse, with a labral incision of variable length and position 

 in the shell. There is no frontal veil between the cephalic 

 tentacles, an epipodial ridge is present, and there is a 

 corneous multispiral operculum. Fischer (5) writes: " Quel- 

 qiies auteurs distinguent deux families, Scissiirellidge et 

 Pleurotomariidae, mais les differences qui existent entre ces 

 deux types n'ont pas plus d'importance que celles qu'on con- 

 state entre les divers groupes de Trochidic. Je les considere 

 comme des sous-families." Pelseneer (13), who had studied 

 their anatomy, retains these forms in the family Pleuroto- 

 mariidae. Yet it is obvious, from what precedes, that the 

 Scissureliidie cannot possibly be retained in this position. 

 The diiferences in the radula alone are sufficient to distinguish 

 the two types. But in addition to this the Scissurellidae 

 differ from the PleurotomariidjB in a number of characters, 

 which may be summarised as follows : 



(1) The Scissurellidas have two columellar muscles; Pleuro- 

 tomaria has only one. 



(2) The eyes of Scissurellidas are closed; thoso of Pleuro- 

 tomaria are open. 



{:5) The subocular tentacles of the Scissurellidae are absent 

 in Pleurotomaria. 



(4) The epipodium of Pleurotomaria is destitute of tentacles, 

 cirrhi, or lappets. 



(5) The wide distance apart of the ctenidia, the large size 

 of the pericardial cavity, the forward position of the ventricle 

 of the heart, and the more distinct shifting of the organs of 



