BuCKMAN. — Terniinnlorin for Brachiopoda. 451 



valve-junction ; but before proposing these it is advisable to consider the 

 general course of development which has led to the specialized foramen of 

 the Telotremata : it is to such foramens that the various terms hitherto 

 proposed apply. 



(1.) The pedicle-opening or delthyrium is unmodified, and is there- 

 fore in area coextensive with what may be called an o])ening or 

 foramen. 



(2.) Tlie pedicle-opening is modified by the growth of various plates, so 

 that the area of the foramen is less than the area of the delthyrium. 



(3.) The pedicle-opening moves, as new test is deposited, away from the 

 apex towards the posterior margin, and the abandoned track is 

 closed by a plate called a " listrium " (Discinacea). 



(4.) The pedicle-opening moves in the opposite direction, out of the 

 delthyrial area, by the pedicle gradually absorbing the apex. 

 This is the development found in submesothyrid to epithyrid 

 Telotremata. 



Now, as the modifications of the foramen take the form of constricting 

 the area or a shifting of position, it may be seen that the terms " Neo- 

 tremata," and so forth, which suggest something bored out, are not 

 altogether appropriate. Only in the last case, where old test is removed, 

 is there anything like the process of boring. Closing up a space so as to 

 reduce a hole is something quite distinct from boring out. However, that 

 point is not for consideration now.* What has to be dealt with is what 

 may be called the character of the foramen. 



When the foramen and the delthyrium correspond the foramen might 

 be said to be delthyrid in character. When the foramen is less in area than 

 the delthyrium, by the growth of various plates which modify the delthyrial 

 opening, then the term constricted foramen seems appropriate. When the 

 foramen is shifting or has shifted its position more or less out of the 

 delthyrial area, then the foramen is in its character migrcmt or migrate., as 

 the case might be. The mesothyrid Telotremata have migrant foramens, 

 and the epithyrid, migrate. When the foramen moves as new territory 

 is developed it may well be called emigrant, and when it goes to take up old 

 territory — the Terebratuloids — it could quite well be said to be immigrant. 



Using the term " foramen/' therefore, in the above general sense as 

 the pedicle-opening, which in character may be unmodified, modified, or 

 migratory, it is necessary to define its position with regard to the line 

 of the valve-junction. It is situated in the ventral valve, and the obvious 

 term would be 



Gastrothyrid {yaa-Trjp, belly). All the position-terms, " hypothyrid," 

 " mesothyrid," " epithyrid," relate to and are more precise locations of the 

 foramen in gastrothyrid Brachiopoda. 



If the foramen were situated in the dorsal valve, then the term would be 



Notothyrid (vtoios, back). I know no such case ; but according to 

 the statement in the review above noticed the hypothyrid position would 

 be notothyrid. It is, however, gastrothyrid, and hypothyrid because under 

 the apex. 



Then there are cases in which the foramen is situated at the junction 

 of the two valves, part of the foramen being in each valve. For this it is 

 not so easy to obtain a suitable term, but I would suggest 



* It miglit be suggested, however, that " Eotremata " would be preferable to 

 " Atremata." understanding Tpr}/j.a in the .sense of opening. 



15* 



