PACIFIC COAST SPECIES. 



91 



Jaw and teeth of If. Laiisingl. 



The first impression giveu by 

 the jaw is that it bears narrow 

 separated ribs as in Bulimu- 

 lus, Cylindrella, &c. A more 

 careful study of it, however, 

 shows the ribs to be very 

 broad, crowded, flat, with 

 narrow interstices between 

 them. 



Lingual membrane with 

 17_1_17 teeth; 6 laterals 

 on each side. Centrals (Fig. 

 B) with the base of attachment longer than wide, the lower lateral 

 angles expanded; upper margin broadly reflected; reflection very short, 

 tricusi)id ; side cusps decidedly developed, short, bearing distinct 

 cutting points ; median cusp long, slender, bulging at sides, reaching 

 nearly to the lower edge of the base of attachment, beyond which 

 projects the long, distinct cutting point. Laterals like the centrals, 

 but asymmetrical by the suppression of the inner lower angle of the 

 base of attachment, and inner side cusp and cutting point. Mar- 

 ginals (C) aculeate, their bases of attachment less sole-like than in 

 Zonites, but more circular in outline. C shows these bases of at- 

 tachment. D gives one marginal tooth in profile. 



This is the first known instance of a species with ribs on its jaw hav- 

 ing aculeate marginal teeth, or of a species furnished with ZonitesAike 

 shell having decided ribs upon the jaw. It will be difficult to find a 

 place for the species under any description of genus or subfamily. 

 The shell is that of Zonites, but that genus has a ribless jaw with 

 median projection. It will be seen that its ribbed jaw and aculeate 

 margnial teeth do not sustain my assertion that for the larger divis- 

 ions these organs may be relied on as systematic characters. The 

 result of my examination of this species was as unexpected as it is 

 puzzling. It proves, however, that the development of the terrestrial 

 niollusks has been too irregular to admit of our expressing it in any 

 satisfactory system of classification. 



Micropliysa Stcarnsi, Blaxd. 



It is larger, more elevated, and more distinctly striated than Micro- 

 physa Lansiiigi, has 7 whorls, with rather wider and more rounded aper- 



