140 FISSURELLID^E. 



of the back is somewhat obscurely concentrically waved ; over the 

 sculpture the shell has a polished appearance ; margins thin, sharp ; 

 interior smooth, somewhat polished ; the scar of the pedal muscle 

 narrow, a considerable distance within the margin, the anterior ends 

 of the scar enlarged, hooked backward on their inner edges ; these 

 ends connected by a line broadly arched forward and marking the 

 attachments of the mantle to the shell over the head. (Dall.) 



Family FISSURELLID.E. 



Shell conical, limpet-shaped, non-spiral, (but with a spiral nucleus), 

 having a perforation, anterior slit, notch or emargination for the 

 passage of the anus ; not nacreous ; having a horseshoe-shaped im- 

 pression of the adductor muscle ; bilaterally symmetrical. Animal 

 bilaterally symmetrical externally, the anal orifice on the median 

 line either anterior, central or posterior. Gills paired, one on each 

 side of the back, their free ends extending to the neck ; muzzle stout ; 

 eyes on peduncles of variable length at the outer bases of the ten- 

 tacles ; mantle continuous or slit anteriorly ; foot fleshy, bearing 

 generally a row of epipodial papillse. Adductor muscle horseshoe- 

 shaped, open anteriorly. Radula with central, lateral and uncinal 

 teeth, the laterals usually 5 in number, narrow except the outer one 

 which is very large with a strongly recurved and denticulated cusp. 

 Uncini numerous as usual in the Rhipidoglossa. 



The classification of this very natural and well-defined family is 

 still in an unsatisfactory condition, owing to the lack of knowledge 

 regarding the animal. I have examined all of the alcoholic 

 material accessible to me, and have freely used the results of my 

 work, in combination with the observations of others authors, in the 

 formation of generic groups. The dentition does not exhibit 

 great diversity, and will need still more study before the value of 

 certain characters can be regarded as settled. For this reason, and 

 because the limits of my work forbid full illustration of the radulse I 

 have studied, I have deferred any detailed discussion of the dentition. 

 I may, however, call attention here to the reliance I have placed on 

 the form of the rhachidian tooth as a diagnostic character of my 

 subfamily Fissiirellince. It may also be noted that in most 

 EmarginulinoB the odontophore is bilaterally asymmetrical, a unique 

 and anomalous arrangement. 



I believe that the genus Fissurella (as restricted herein) represents 

 the latest modification of this family. I have seen no fossil species 

 belonging to it. The Emarginulince include the more primitive 



