﻿SUPPLEMENT TO THE BRITISH 



strange to say, no other example appears to have been discovered than the one picked 

 up by Mr. Bean some time previous to 1835. 



In 1855 I described and figured, under the above designation, a much smaller shell, 

 which occurs very abundantly in the Upper Greensand of Cambridge, and of many 

 other places. It is very persistent in its smaller proportions ; and the longitudinal radiating 

 strias which cover the surface of both valves are likewise much stronger or coarser, in 

 comparison with those in the typical T. lineolata of Phillips. Mr. Meyer and some 

 other Palaeontologists have consequently expressed themselves uncertain whether the 

 two forms should be united in a single species ; and it became quite evident that the 

 Cambridge shell should be distinguished, at any rate, by a varietal designation. 



80. Rhynchonella lineolata, Var. Carteri. Dav., Cret. Mon., PL XII, figs. 7 — 10. 



This variety has, for many years, been labelled Rh. Carteri on a tablet in the 

 British Museum. It has also been figured and described under the name of Rh. lineolata 

 by Dr. Schloenbach in 1867 (' Uber die Brach. der Norddeutsch. Cenoman-Bild. Geognost.- 

 Pal. Beitrage,' vol. i, p. 493, pi. xxiii, fig. 4) ; also by Pictet in his ' Brach. du Terrain 

 Cretace de St.-Croix,' p. 48, pi. cc, fig. 14, 1872. Dr. H. B. Geinitz names it likewise 

 Rh. lineolata in his 'Das Elbthalgebirge in Sachsen,' pi. xxxvi, fig. 36, 1872. 



This variety, which occurs so plentifully in the Upper Greenand of Cambridge, has 

 been found, with the same small proportions and other characters, in beds of a similar age 

 in Germany and Saxony. M. Pictet quotes it from the Gault of Switzerland, and I have 

 found it in Upper Neocomian beds at Drap and Layet, near Nice, in the South of Prance ; 

 hence it would seem to have enjoyed a rather extended geological range. The Rev. T. 

 Wiltshire has found this form in the Red Chalk of Speeton. 



Rhynchonella dimidiata, Sowerby. 



In his memoir, ' Ueber die Brach. der Norddeutsch. Cenoman-Bildungen,' p. 486, 

 1867, Dr. Schloenbach insists that the specimens I have drawn in PI. XI, figs. 1 to 14, 

 and PL XII, figs. 24, 28, 29, 30, are all referable to a single species, namely, T. dimidiata, 

 Sow. Dr. Schloenbach may be correct in the view he has taken (with the exception of those 

 in PI. XII, figs. 28 — 30) ; but, if so, then an unusually great variability must be conceded 

 to the species under description ; for it would be made to include forms differing very 

 considerably in shape and sculpture, individuals with strong ribs and others with 

 numerous small ones being all combined under a single denomination. When describing 

 the shells alluded to by Dr. Schloenbach I remember feeling greatly puzzled, and some 

 uncertainty may still prevail. 



