GASTRIC TEETH. 



107 



Symbols 



DEXTRALS. 



Right 



position . 



.SINISTRALS. 



) 



As placed on 

 the plate. 



Svmiolt 



| posi 



ic 



ght 



tion. 



As placed on 

 the plate. 



2. f Orchard Quarrv. 



3. J 



5 ' j-Carnpsie. 



y' j Orchard Quarry. 



13 1 



, V J- Orchard Quarry 



16. 



^Orchard Qi 



19 1 



," >Newcastle-ou-Tyne. 



9.1 

 -, ,-.' J-Cowlands Quarry. 



, 9 'l Dolly Quarry. 



1 7 1 



' ^Orchard Quarry. 



9 .' hRedesdale. 1 



7,'q Eedesdale. 1 

 33. 



34 



Cock of Arran. 



" iRedesdale. 1 



27. Orchard Quarry. 



30. 



31. 



^East Kilbride. 1 



32. Orchard Quarry. 



37 1 



g 8 " \ Orchard Quarry. 



^•jOrchard Quarry. 



43. Dunbar. 



Ouel 

 in [ 

 44. 



Londonderry. 1 



^•JRedesdale.i 



41. Orchard Quarry. 



42. Eccup. 1 

 One] 



in [-Londonderry. 1 

 44. 



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. 



(All on 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 simple 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 ^ means a dextral convexity, with the high cusps forward, or towards 



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



the plate (PI. XXVI) the dextral teeth occur as K(^\ and the sinistrals as r~~\h. 



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), 



