THE BBACHIOPODA. 19 



specimens are absolutely identical, that this is where it is most 

 developed, where the species is most constant and best charac- 

 terised, and where its dimensions are sufficiently big without 

 being very large. That in the Parkinsoni beds it is of largest 

 size, and produces remarkable varieties.* My observations 

 in this district agree with these remarks, only I have not 

 for certain observed it in the Sauzei bed. At Oborne, how- 

 ever, and at other places in the Humphriesianum zone 

 this species is very common, not large but regular and 

 globular, except that sometimes it passes into a rather flattened 

 variation. In the Parkinsoni zone at Broadwindsor and round 

 Bridport, etc., Ter. spJiaeroidalis is found at its finest size, and in 

 all sorts of varieties. The ventral valve is often peculiarly 

 enlarged, another variety has the edges of the valves thick- 

 ened by layers like Wald. Waltoni, and in others the growth 

 seems to have stopped and then to have been resumed, thus pro- 

 ducing large lines of growth. 



In the zone of Murchisonse, however, there come specimens 

 which have hitherto been referred to Tereb. spJiaeroidalis or to 

 Tereb. Eudesi. They are, in fact, between the two, being round 

 and globular, and having the base ornamented with a distinct 

 biplication very much in shape like the biplication of Tereb. Eudesi, 

 but not nearly so pronounced, and it only produces slight furrows 

 in the shell. The specimens do not agree exactly with any of 

 the figures of Tereb. conglobata given by E. Deslongschamps, but 

 much resemble them in all points, except that the biplications 

 are too regular. Whether these specimens should be classed as 

 variations of Tereb. spJiaeroidalis or Tereb. conglobata I am not yet 

 able to determine. 



Dimensions of Tereb. sphaeroidalis Length, 17 ; breadth, 15 ; 

 depth, 15 lines. 



Localities. Bradford Abbas, Oborne, Broadwindsor, etc. 

 (Dorset) ; Crewkerne Station, Gralhampton, etc. (Somerset) . 

 also Dundry (Somerset) ; also Bayeux, Sully, Port-en-Bessin, 

 etc., and in Burgundy, and many other places in Prance, and 



* See Deslongschamps, Brach. Terr. Jurass, page 282. 



