14 PAL/EONTOLOGV 



examining the surface with a lens we fail to find any trace 

 of the pattern of punctations so characteristic of the 

 terebratuloids; but we observe a silky, fibrous appear- 

 ance. Internally, we find still more striking differences. 

 It is true that the cardinal process, hinge-plate and 

 sockets, hinge-teeth and the several pairs of muscle- 

 impressions are all present with only slight differences of 

 arrangement ; but although spiral brachia exist there is 

 no calcareous loop. From the hinge-plate two short 

 processes project into the cavity, and correspond to the 

 beginning of a loop : they are termed the crura (plural 

 of cms). Again, in the umbonal cavity of the ventral 

 valve there are a pair of vertical partitions which, as 

 they extend into and strengthen the teeth, are called 

 dental plates : these, however, are also found in some 

 terebratuloids. 



Forms more or less similar to Hemithyvis psittacea are 

 often found fossil, in the Cornbrash among other strata. 

 In the works of Sowerby they were included under the 

 broad name of Terebratula, but afterwards distinguished 

 by the separate name Rhynchonella by Fischer von 

 Waldheim. This name in turn has had to be restricted 

 to a portion only of these forms, but we can still con- 

 veniently speak of them as rhynchonellids . 



Thecidea (Lacazella) meditevvanea is a small brachiopod 

 with a very thick shell. It has no pedicle, but is found 

 cemented to other shells by its ventral umbo. The long 

 and narrow delthyrium occupies the middle of a large 

 cardinal area, and is completely closed up, not by a pair 

 of plates, but by a single one (deltidium). Internally there 



