JURASSIC AND TRIASSIO BRACHIOPODA. 209 



212. Rhynchonella lineata, Young and Bird. Dav., Ool. Mon., Plate XVI, figs. 



1 and 3 (only) ; Sup., PI. XXIX, 

 figs. 17, 18. 



Terebratula lineata, Young and Bird. Geol. Survey of the Yorkshire Coast, 



p. 232, pi. viii, fig. 10, 1828. 

 — triplicata and T. bidens, Phillips. Geol. of Yorkshire, pi. xiii, 



figs. 22—24, 1829. 

 Rhynchonella variabilis, var. Dav. British Ool. Brach., p. 78, pi. xvi, figs. 1 and 3, 



1852. 

 — triplicata, Simpson. Foss. Yorkshire Lias, p. 131, 1855. 



Rhynchonella lineata, Tate. The Yorkshire Lias, p. 421, pi. xv, figs. 21, 22, and 



23, 1876. 



This is a much larger shell than B. variabilis proper, and since Messrs. Tate and 

 Blake have devoted so much attention to the shell in question in their admirable work 

 on the " Yorkshire Lias," we may as well reproduce Professor Tate's description. 



" Adult forms of this species have a resemblance to B. tetraedra, but differ in the 

 number and character of the plaits, and in the larger, less incurved beak, and large 

 foramen. There are invariably two or three plaits on the mesial fold, with from 

 three to four on each lateral area of the brachial valve which are all evanescent 

 towards the umbo. Phillips distinguished two forms, that with three plaits as 

 triplicata, and that having two on the mesial fold as bidens. . . . Young and Bird's 

 description and figure belong to the bidens form ; and as there can be no doubt 

 respecting the shell figured by them, supplemented by a sufficiently full description, 1 

 adopt their name in accordance with the rule of priority. The description reads as 

 follows : ' No. 10 is a small shell, very common in the ironstone bands and in the Dogger ; 

 it differs from T. tetraedra not only in being smaller, but in having only two elevated 

 plaits at the base, and a sunk line on the lesser valve, running from the beak to a groove 

 between these plaits. There are about four plaits on each side of the beak, besides 

 those of the base.' As regards size, however, it not unfrequently equals the largest 

 specimens of Bh. tetraedra." 



Professor Tate then alludes to the denticulated sockets (Sup., PI. XXIX, fig. 18), "a 

 character which also belongs to B. rimosa and B. acuta ; vide Quenstedt's ' Die 

 Brachiopoden/ t. xxvii, figs. 107 and 151. The young shells are depressed, broadly 

 subtriangular ; the front edge of the united valves is at first straight, but gradually 

 becomes arched as the shell is enlarged ; no trace of plication is presented by specimens 

 up to half-an-inch in breadth. The beak is erect, and the foramen large. There is no other 

 alternative between regarding these small shells as the young of B. lineata and assigning 

 them to a new species, as they are found in company with B. lineata in the shales below 



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