Vol. 60.] EH.ITIC OF THE SOUTH-WALES DIRECT LINE. 



205 



Dimensional 



('. crassiuscula. C. concinna. 



. / horizontal \ - , 



lal ratio .,)... £ or less. 2*2 or more. 



\ vertical / 6 



Position of beak (from anterior)... Never less than 4-. \ to X- of length 



o -1 o o • 



The other characters are the same for both, namely : small and 

 non-prominent beak, general oval form, rounded anterior margin 

 and gently convex lower margin. 



It is, however, just at our Rhaetic forms that the above distinc- 

 tions break down ; for, in dimensional ratio and position of beak, 

 our form might be considered to be either a crassiuscula-like muta- 

 tion of concinna, or a concinna-like mutation of- crassiuscula. In 

 fact, any distinction based upon the numerical ratio of dimensions 

 is confessedly artificial ; in our case, these distinctions would 

 separate the young form (shown by the growth-lines), as a typical 

 crassiuscula, from the adult form, which approximates to concinna. 



It seems best to group our forms broadly under C. concinna, 

 which may be considered to connote : elongate oval form, uniformly- 

 and strongly-convex anterior and posterior margins, and uniformly - 

 but gently-convex lower margin. 



The figure which most nearly approaches our form is that of 

 0. regularise Terq. (4), pi. xx, fig. 2, which agrees remarkably well 

 in all respects, except that the convexity of the anterior margin is 

 greater (in the figure) than that of the posterior margin. 



Specimens are common in the main Avicula-beds. 



Pleurophorus eloxgatus, Moore ('? = Anoplophora postera, Deffuer 

 & Fraas). (Text-fig. 5.) 



There is no doubt as to the identity of our fossils with Moore's 

 species (1); the general contour, and the fold which runs diagonally 

 backward, render recognition easy. There is, however, more 

 difficulty as to the genus. 



The cast exhibits the following characters : — Upper and lower 



margins nearly parallel, but 



Fig. 5. — Pleurophorus elonga- slightly diverging backward ; a 



tus, Moore (magnified Ik prominent anterior muscular im- 



cliameters). pression, in front of the beak. 



circumscribed by a deep furrow ; 

 a pallial line of continuous curva- 

 ture, ending in a less prominent 

 posterior muscular impression : a 

 very blunt beak-region ; a sharp 

 indentation, in front of the beak, 

 continuous with the deep groove 

 which forms the hinder boundary 

 of the anterior muscular impression. All these characters of the 

 cast, except the blunt beak-region, would apply to any one of the 

 genera Pleurophorus, Anoplophora, or Mijoconcha. 



Since Anoplophora has no teeth, and Myoconcha only a long ridge- 

 like tooth, running backward from the beak close along the hin^e- 



