20 NOTES ON THE BRITISH JURASSIC BRACHIOPODA. 



safely infer that the brachiopods of ancient times, like 

 those of tlie present day, lived, some in very deep water, 

 othei's in water of moderate depth, while others again lived 

 in comparatively shallow water. 



The recent forms are apparently gregarious, and being 

 vei-y prolific, they usually occur in vast numbers in tbeir 

 favourite haunts (10, p. 336). The same may be inferred 

 respecting the fossil forms, which no doubt lived under very 

 similar conditions. Unmistakeable evidences of this are to 

 be found in the Jurassic rocks of England. In the Middle 

 Lias Marlstone-rock of some parts of the Midland counties 

 Rhynchonella tefraliedra and Terehratula punctata and its 

 al'lies occur in such numbers as to practically constitute 

 distinct beds. The same may be said of the Upper Trigonia- 

 grit of the Cotteswolds which is literally crowded with 

 Acanthothyris (Jxhyn.) spinosa, Ter. glohata, and other brach- 

 iopods. The Ooliticmarl of the Cotteswolds, particularly 

 at Wall's quarry, near Brimscombe, is another instance 

 in point ; in fact at some levels it is not much unlike 

 a conglomerate of Ehyn. suhohsoleta and Ter. fitiibria. 



An interesting point in connection with the Brachiopoda 

 is their great variability in size, shape, ornamentation, and 

 thickness of shell. 



In size they vary from the microscopic Thecidea and 

 Zellania, found in the upper beds of the Inferior Oolite 

 of Dundry, up to the giant Pi-oductus of the Carbonifei'ous 

 period, one specimen of which (Productus giganteusy, figured 

 by Davidson, was nearly a foot in breadth by something 

 less in length. 



Their variability in shape is quite proverbial, and every 

 student of this group of shells will be prepared to endorse 

 the remarks of Davidson, that " So great is the modifica- 

 tion in shape in the same species and in the larger number 



