196 SUPPLEMENT TO THE BRITISH 



183. Rhtnchonella lacunosa, Schloth. Suppl., PI. XXVI, figs. 13, 14. 



Terebratulites lacunosa, Schlotheim. Beitrage fur Nat. Vers, in Leonhard's Min. 



Tasch., vol. vii, pi. i, fig. 2, 1813. 

 Terebratula — Von Buck. Ueber Ter., p. 49, 1834, and Mem. Soc. G6ol. 



de France, 1st ser., vol. iii, p. 150, pi. xv, 



fig. 22, 1838. 



— — Bronn. Index Pal., p. 1239, 1848. 



— — Quenstedt. Die Jura, p. 632, pi. lxxviii, figs. 15,16,1858. 



— — Quenstedt. Die Brachiopoden, p. 121, pi. xxxix, figs. 77 — 



107, 1871. 



As stated under Rh. tetraedra (of this Supplement), my identification of this species 

 at p. 96 of the Monograph on ' Fossil Brachiopoda ' was incorrect, and requires to be 

 erased, for the shell there described subsequently proved to be a variety in form of 

 Rh. tetraedra, from the Lias of Dunrobin, in Scotland. 



I am acquainted with two examples only of Rh. lacunosa from the Jurassic Rocks of 

 Great Britain ; one from the Lower Calcareous Grit of Beedall, Wykham, in the Museum 

 of the School of Mines (Sup., PI. XXVI, fig. 13) ; and another, from the same formation 

 at Oliver's Mount in Yorkshire (same plate, fig. 14), was communicated to me by Mr. 

 Hudleston. Some internal casts found by Mr. Judd in the Upper Oolites of Alt-na-cuil 

 in Sutherland may also probably be referable to Schlotheim's species ; and a good series 

 of specimens may be seen in the Dunrobin Museum. 



The material at our command is not quite satisfactory; for, although those British 

 specimens are in all probability referable to Rh. lacunosa, they do not exhibit the charac- 

 teristic shapes of the shell. It is, I am ready to admit, a most variable shell, and, 

 indeed, group of shells, for Quenstedt has divided it into many named varieties, such as, 

 var. decorata, var. dijissa, var. multiplicata, var. polita, var. rariplicata, var. rupicaleis 

 var. silicea, var. sparsicosta ; and to one of these our British examples may be referred. 



In external shape Rh. lacunosa is more or less sub-pentagonal, slightly wider than 

 long ; dorsal valve more or less convex, and usually divided into three lobes, of which the 

 central one is more or less elevated, forming generally a slightly flattened mesial fold ; 

 beak moderately produced, and incurved, with a circular foramen under its angular 

 extremity, margined and slightly separated from the hinge-line by small deltidial plates. 

 Ventral valve convex, with a wide sinus of moderate depth. Surface of each valve 

 covered with a variable number of angular ribs, of which a few sometimes bifurcate 

 near the margin. The largest known British example measures — length 11, width 

 12, depth 8 lines, but the full-grown shell acquired larger proportions. 



This species has a considerable geographical range. It was found abundantly by the 



