9G 



THE GEOLOGIST. 



ON NEW BRACHIOPODA, AND ON THE DEVELOPMENT 

 OF THE LOOP IN TEREBRATELLA. 



By Chaeles Moore, F.Gt S. 



(Continued from page 445, vol. iii.) 



Thecideum. Defrance. 

 Thecideum omatum. Moore. PL, ii., figs. 1 — 3. 



Shell inequivalve ; punctuate, rather rugose, front deep, rounded ; 

 attached by a considerable portion of the ventral valve ; beak slightly 

 incurved ; deltidium small and depressed. The ventral valve is flat- 

 tened on its under side. Its interior is surrounded by an elevated, 

 slightly granulated margin. Under the deltidium are seen two 

 raised oval processes, separated by a longitudinal septum, which 

 occupies the greater length of the shell. The exterior of the dorsal 

 valve is rugose and flattened. The interior possesses a narrow, thin, 

 punctuated margin, immediately succeeding which is a ridge of single 

 granulations, which are stronger towards the frontal margin, gradu- 

 ally disappearing as the ridge passes upwards. Springing from the 

 centre of this granulated ridge is a septum, slightly tapering from its 

 base, on either side strongly serrated, between which is a central 

 longitudinal groove. The septum occupies nearly the whole height 

 allowed by the cavity of the shell, and divides it to nearly three- 

 fourths of its length. From the top of the septum there are thrown 

 off two extremely delicate lamellae, forming a loop which curves 

 downwards towards the front of the shell, where they bifurcate, and 

 are then again united to the shell at its inner sides. Above the sep- 

 tum and attached lamellae a band occurs, forming a bridge over the 

 visceral cavity. This is united to the granulated ridge, which thus 

 completely surrounds the inner portion of the valve. 



Obs. — The preservation of the loop as shown in the enlarged 

 fig. 3, plate ii., is remarkable, since in the original specimen it is in 

 substance scarcely thicker than the finest unspun silk, and extremely 

 brittle. The interiors of the Brachiopoda are only to be developed 

 by careful manipulation in dissecting or opening up the valves. 

 Many of the interiors of the Thecididae are very beautiful ; but I 

 have never as yet seen any species equalling in delicacy of structure 

 that under consideration. It is from the Coral Rag of Lyneham; 

 Wilts, where it is not uncommon. 



Thecideum pygmoevm. Moore. PI. ii., figs. 4 — 7. 



Shell microscopic, longitudinally oval ; both valves convex ; 

 attached to other bodies at the upper part of the ventral valve ; beak 

 slightly produced ; area short ; deltidium ill defined. A thin raised 



