■220 
DESCRIPTION OF THE FOSSILS. 
S. imbricata. Sow. Ph. PI. X. fig. 20. Bolland; Derbyshire; Northum- 
berland. 
I ransversely elliptical, mesial fold indistinct or none ; surface with strong radiating 
striae, interrupted by concentric imbricating laminae. 
E. Ter ebratuli formes. Cardinal urea none. 
S. fimbriata. Ph. Florence Court. 
Orbicular, depressed, beak of the lower valve prominent, but small ; surface strongly 
radiated and concentrically imbricated. 
S. planosulcata. Ph. PI. X. fig. 15. Bolland ; Queen’s County. 
Pentahedral, depressed, middle of each valve planosulcate. 
S. expansa. Ph. PI. X. fig. 18. Bolland. 
No mesial fold ; depressed, concentrically striated, with fine radiations. 
S. glabri stria. Ph. PI. X. fig. 1 9 . Bolland. 
Mesial fold prominent ; depressed ; fine radiating striae (the latter character varies). 
S. squamosa. Ph. PI. X. fig. 21. Kendal ; Florence Court. 
Depressed ; mesial ridge small ; transversely imbricated ; smooth. 
S. globularis. Ph. PL X. fig. 22. Bolland. 
Subglobose ; smooth ; mesial fold broad. 
S. elongata. Ph. PI. XI. fig. 9. Bolland. 
Pentahedral, smooth, with obtuse radiations. 
F. Filosw. Surface with prominent radiating threads. 
S. resupinata. Mart. Sow. PI. XI. fig. 1. Bolland ; Greenhow hill ; 
Hawes ; Otterburn ; &c. ; Derbyshire. 
Transversely elliptical ; lower valve undulato-concave ; upper valve flattened in the 
middle. Surface finely radiated with stri;r which rise at intervals to prominent spinous 
lines. 
S. connivens. Ph. PI. XI. fig. 2. Bolland, 
Subglobose, margin undulated ; radiating strife rather coarse. 
S. filiaria. Ph. PI. XI. fig. 3. Bolland ; Fountains’ fell ; Derbyshire : 
Otterburn. 
Very depressed, elongate ; hinge line abbreviated, radiating stria fine. 
S. arachnoidea. Ph. PI. XI. fig. 4. Stradone ; Haltwhistle ; Alien- 
heads ; near Hesket-Newmarket. 
Very depressed, truncato-orbicular. Plinge line wide as the shell ; strife fine, sharp, 
and continually subdivided ; upper valve convex as in S- resupinata. 
S. radialis. Ph. PI. XI. fig. 5. Florence Court ; Cumberland. 
Very wide, semielliptical, hinge straight, front circular ; strong radiating ridges, 
and intervening smaller ones, crossed by imbricated lamella 1 . 
