GASTRIC TEETH. 



19? 



> 



X 



Si/mboh 



i 



DEXTRALS. 



Right 

 Ijositiou. 



i) 



^•1 



2. ^Orchard Quarrv. 



g' ^Campsie. 



»■ J-Orchard Quarry. 



/.■ [-Orchard Quarrv. 



,p' [Orchard Quarry. 



., ■ -Newcastle-ou-Tyiie. 



^^' -Eedesdale.i 



27. Orchard Quarry. 



^^•"j-East Kilbride.i 

 SI. I 



32. Orchard Quarry, 

 oo' > Orchard Quarry. 



^g-jOrchard Quarry. 



As placed on 

 the plate. 



9 1 

 ■^Q j-Cowlands Quarry. 



•.f,' V Dolly Quarry. 



17 ^ 



,„■ [-Orchard Quarry. 



9 ," medesdale.^ 



qV .'■Eedesdale.^ 



33 1 



oj' j-Cock of Arrau. 



„,." j-Redesdale.i 



41. Orchard Quarry. 



42. Eccup.i 



Oue] 



in VLondonderrv.^ 

 41. J 



1 At these localities the gastric teeth are found 

 under two conditions ; some free, and others still 

 within the carapace, as shown by their protruding 

 through the valves. 



43. Dunbar. 



One] 



in iLondonderry.i 



44. J 



(All ou PI. XXVI are magnified two diameters, except figs. 1 — 7.) 



By way of making it easy to recognise the relative position of these gastric 

 teeth in the original stomach, as pointing fore and aft (that is, from its cardiac or 

 front to its pyloric or hinder division), we introduce a simjjle symbol. The 

 crescent refers to the curvature of the tooth, and the little angle, or angular sign, 

 shows at which end the coarser cusps rise out of the tooth. 



Thus j means a dextral convexity, with the high cusps forward, or towards 

 the cardiac extremity of the stomach ; and ^ indicates the sinistral position. On 



the plate (PL XXVI) the dextral teeth occur as \/^~~\ and the sinistrals as ,^^A. 



There are probably distinctions due to the relative age of individuals in the 



collection, but we cannot point with certainty to any specific differences among 



the figured specimens, except that figs. 33, 34, and 35, 36 (not quite perfect). 



