PACIFIC COAST SPECIES. 113 



An European and Mediterranean genus, found also in the Canaries 

 and at Teneriffe. In North America it is only represented in the Cali- 

 fornia Eegion, and by one species only. 



Von Martens describes the jaw of Gonostoma as having- distinct ribs. 

 Moqnin-Tandon so figures that of obvohita, Mlill., lenticula, Fer., and 

 E(ntgiana,F6r.: and Gassies (Journ. de Conch., 



•^ ' ' ^ ' Fig. 79. 



XY, 1867, 15) so describes that of H. constricta^ 



B. Our single species has a jaw (Fig. 79) low, 



wide, slightly arcuate, ends scarcely attenuated, 



blunt ; cutting margin without median projection ; •^'^^^ °^ ^- ^"''^"i- 



anterior surface with a strong transverse line of re-enforcement, and 



numerous (about 12) wide, crowded ribs denticulating either margin. 



The lingual membrane of obvoluta is described by Goldfuss (1. c, 45) 

 with a type of central teeth differing from that I have shown in Yafesi. 

 This last has its lingual membrane (Terr. Moll., V, Plate Y, Fig. Q) long 

 and narrow ; teeth 24-1-24, with 6 perfect laterals. Centrals with the 

 base of attachment longer than wide, with expanding lower lateral an- 

 gles and squarely reflected upper margin ; reflection large, stout, bear- 

 ing small but distinct side cusps, with short, blunt cutting points, and 

 a long, stout median cusp reaching the' lower edge of the base of at- 

 tachment, beyond which projects the longi acute cutting point. Laterals 

 like the centrals, but asymmetrical by the suppression of the inner, 

 lower, lateral angle of the base of attachment, and the distinct inner 

 side cusp and cutting point. Marginals subquadrate (6), a simple 

 modification of the laterals, the reflection being more developed, and 

 bearing one inner, oblique, long, blunt cutting point and one smaller 

 side cutting point ; the extreme marginals (c) are rather wider than 

 high, and the cutting points are bluntly rounded. 



Oonostoina Yatesi, J. G. Cooper. 



Shell globosely planulate, equally depressed above and below, widely 

 umbilicated, thick, smooth, scarcely marked with incremental strias, 

 ' horn- colored ; spire sunken, apex obtuse; whorls 6J, _^"";„ ^- 

 slightly convex, each one raised above the preceding one, 

 the last tumid, obsoletely carinated, descending at the 

 aperture ; aperture oblique, lateral ; peristome thickened, 

 white, its extremities far removed, scarcely reflected, above 

 deflected and sinuous ; umbilicus very wide, showing- 

 all the whorls. Greater diameter 9, lesser 7™'" ; height, 



^ O. Yatesi. 



1749— BuU. 28 8 



