Meyer — On Cretaceous Brachiopoda. 271 



attachment of the loop. This evidence consisted in the occurrence 

 of a curved line or ridge extending on the sides of the septum from 

 its origin beneath the hinge-plate to the point from vv^hence the 

 transverse processes then proceeded for the attachment of the loop. 

 And as such ridges are not observable in any species of Waldheimia 

 with which I am acquainted, they may, I imagine, be regarded as 

 the remains of former processes from the septum, indicative of the 

 attachment of the loop from its earliest development. 



The condition of the loop and septum in some very young speci- 

 mens of Terehratella Menardi, in my collection, fully tends to sup- 

 port this evidence. 



In these examples the septum is much elevated, and extends to 

 nearly the front of the smaller valve. The descending portions of 

 the loop, which diverge from the hinge-plate in the usual way, are 

 broadly attached to the septum near its extremity, and bending 

 sharply rise in an almost inconspicuous ridge above the septum. 



From this stage of the loop its development would probably 

 follow what appears to me to be the natural law of increase in the 

 loops of Brachiopoda, namely, the gradual absorption of the inner 

 edges of the loop, and the increase of its outer or upper edges by the 

 secretion of fresh shelly-matter from a portion of the lining mem- 

 brane of the shell. 



With regard, therefore, to the attachment or n(3n-attachment of 

 the loop at different ages of the shell in the sections Waldheimia, 

 Terehratella, etc., the rule appears to be that the loops are either 

 constantly attached to the septum — as in Terehratella, Megerlia, etc., 

 — or constantly free, as in Waldheimia. And although the excep- 

 tion may hold good as regards the young of Terehratella Biiclcmanii, 

 Moore, I am sure that such is not the case with regard to Wald. 

 tamarindus, Sow. 



By grinding down or in other ways partially removing the matrix 

 from the interiors of the valves, I have succeeded in obtaining 

 dissections exhibiting the loops of most of our Cretaceous Brachio- 

 poda, and amongst others of the following species, the loops of 

 which have not, I believe, been as yet described. 



1. Terehratula ovata, Sow. Loop short and simple ; no mesial 

 septum. 



2. Terehratula rugulosa, Morris. Loop short and simple ; no mesial 

 septum. 



3. Terehratula squamosa, Mant. Loop short and simple ; no 

 mesial septum. 



The discovery of the loops of these three species has given me 

 much pleasure, as tending to prove the correctness of Mr. David- 

 son's observations respecting the small generic value of surface- 

 markings on the valves of Brachiopoda. 



4. Terehratida Carteri, Dav. Loop short and simple. 



6. Waldheimia Bouhei (?) D'Archiac. {Ter.faha (?) (Sow.)^ 

 Loop much elongated and reflected. Frontal extremity of loop 



1 Figured in Geol. Mag., Vol. I., PL XII., Figs. 5-7. 



