240 ORGANIC REMAINS. 



scar, and a few other spots. It is commonly smoother than g. 

 incurva, and considerably broader, with a lobe on one side. The 

 lobe is sometimes very faintly marked, but is more frequently 

 distinct. Shells of this species are found in a seam of yellow sandy 

 marl, at Rowlston scar, not petrified, but preserved i while others 

 occur there petrified, in the calcareous sandstone.^ — ^A shell like g. 

 incurva, deeply striated or sulcated transversely, occurs in the chalk; 

 but we have not ascertained its genus. 



Perna. Shells of this genus, resembling those figured by Sow- 

 erby. Tab. 66, but much larger, occur in the oolite, at Thornton and 

 other places. They are apt to be confounded with the solens ; 

 especially as it is very difl&cult to obtain a complete specimen, the 

 shell being converted into a brittle spar. 



Pinna. This shell is not very abundant in our strata, yet we 

 have two or three distinct species. 



No. 5, PI. X, occurs in the calcareous sandstone under the 

 oolite, at Scarborough, Palsgrave, Silphoue moor, and other places. 

 It is bent and tapering, like a goat's horn, which it resembles in 

 colour, and in its angled shape, the middle of each valve rising in a 

 longitudinal ridge, so that the cross section is somewhat quadrangu- 

 lar. It has longitudinal striae, or slender ribs, towards the beaks ; 

 but the ribs gradually become obsolete, and entirely disappear towards 

 the base ; where it is marked with transverse strise and wrinkles. 

 The shell is often much wrinkled, presenting a rugged appearance, 

 especially near the base, which is rather truncated. The two valves, 

 in the specimen figured, are parted near the base, where the shell is 

 very thin. It is six inches and a half long, and the base is two inches 

 and a half broad. This species resembles the p. incurva of Linnaeus, 

 but may be fitly named p. capricornus. 



No. 6 displays the inside of a valve of an elegant pinnite, from 

 the lowest shale at Robin Hood's Bay. It occurs in the same shale 



