310 PLACIPHORELLA. 



p. 210. Not of Gould. 



This form is known to me by the valves of a single individual, no. 

 106,922 of the Smithsonian register. It differs from P. velata in 

 the greater prominence of the lateral ribs, the curiously excurved 

 teeth of the side insertion-plates (fig. 15), the less calloused interior 

 of the posterior valve, and its very different form. Compare fig. 9 

 with fig. 16, the former representing the tail valve of P. velata, the 

 latter that of P. borealis. Some other differences are indicated in 

 the descriptions. In this specimen the slit on one side of the pos- 

 terior valve is nearly obsolete. 



P. BLAINVILLII Broderip. PL 66, figs. 26-32. 



Shell ovate, very broad, depressed; variously clouded, streaked^ 

 and maculated with rosaceous and olivaceous or red-brown, gener- 

 ally tessellated at the sutures. 



Median valves hardly beaked. Jugal areas sometimes defined by 

 an obsolete v-shaped sulcus. Central areas appearing a trifle and 

 most minutely granulate under a lens, otherwise smooth and shining. 

 Lateral areas slightly swollen, concentrically marked by ribs of 

 growth ; margins of valves rounded, the sutures not very deep 

 except in young specimens. Posterior valve having the mucro pos- 

 terior, almost terminal ; the posterior sinus of the valve wide and: 

 shallow. 



Interior : anterior valve having 8 slits, the teeth rather short and' 

 roughened or crenulated outside. Posterior valve having a single 

 slit on each side. Median valves with 1 slit; the sutural-plates 

 rather straight and narrow, sinus a shallow wave. 



Girdle thin, very broadly expanded, in front, narrow and not 

 sinuous behind. Surface having sparse, comparatively short hairs,, 

 which in drying become appressed on the girdle, each hair appearing 

 scaly under the microscope, like a snake's skin (fig. 28). The hairs 

 are not especially sutural in position, suture-pores being absent in 

 adult examples ; nor do hairs occur in bunches anywhere. Besides 

 these scaly hairs, there are scattered chaffy hairlets (which in one 

 specimen more contracted than the rest are gathered into little 

 bunches.) 



Length 50, breadth 36 mill. ; divergence 147. 



Inner Lobos Island (Lobos de Tierra), Peru, on stone in 17 fms. 

 (Cuming.) 



Chiton blainvillii BROD., P. Z. S. 1832, p. 27. SOWERBY, Conch. 



