BucKMAN. — Terminology Jor Foraminal Development in Terebratuloids. 131 



use of the terms " dorsal " and " ventral valves " in Brachiopods. As it 

 happens, these shells are so generally examined and depicted in dorsal view- 

 that one imconsciously comes to think of the dorsal valve as the front. 

 Really it is the behind valve, and so the beak-ridges of Bouchardia unite 

 behind (dorsally of) the foramen, which is thus in front (ventrally of) the 

 apex. 



The terms which I have proposed are designed to meet this and similar 

 cases — that is, to express directly the position of the foramen in regard 

 to the beak-ridges ; for there is development in its position — the pedicle 

 shifts from the pseudo-area, cuts through the beak-ridges, destroying the 

 apex, and takes up a position in the ventral umbo. The terms are modi- 

 cations of Phillips's old generic names Hypothyris, Epitkyris, bestowed 

 originally to mark just such difierences in the position of the pedicle. 

 Thus the foramen is — 



(1.) Hypothyrid when it is in the pseudo-area, and the apex is intact; 

 this is a usual condition among Rhynclionellacea, but is rare 

 among Terebratulacea : 



(2.) Suhmesothyrid when the apex has been absorbed, yet the foramen 

 lies mainly in the pseudo-area but partly in the ventral umbo ; 

 this is a frequent condition in Terehratulina : 



(3.) Mesothyrid when the foramen lies about equally each side of the 

 beak-ridges, a usual condition in Mesozoic Dallininae : 



(4.) Permesothyrid when little of the foramen lies on the pesudo-area 

 but the main of it is in the ventral umbo, a condition also 

 found in Mesozoic Dallininae and in Terehratulidae : 



(5.) Epitliyrid when the foramen lies wholly in the ventral umbo and 

 the line of the beak-ridges passes dorsally of it ; this is a usual 

 condition in Terebratididae. 



These are five sequent stages in the shifting of the pedicle ventralwards, 

 of which (1) is the earliest and (5) the latest. The beak-ridges make a 

 datum-line for observation. The Dallininae in general occupy an inter- 

 mediate position between the bulk of RhynchonelUdae and the bulk of 

 Terehratulidae — at any rate, so far as Mesozoic species are concerned. 



There are, however, still other features connected with the foraminal 

 development which require technical terms. As the pedicle absorbs the 

 apex, eating through a line of strong beak-ridges in shifting its position, 

 the ends of the beak-ridges remain like little darts projecting on each side 

 of the foraminal opening — foramen telate. At a later stage these darts 

 become worn off — foramen attrite, well seen in Magellania. Still later 

 the opening is finished ofi with a deposit of test, a kind of rim' — foramen 

 marginate ; and in further development a lip is projected over the dorsal 

 umbo — foramen labiate. This lip seems to indicate that the pedicle has 

 more than attained its farthest limit ventralwards, and that it is now 

 beginning to return on its path to take up a position more dorsalwards. 



These modifications of the condition of the pedicle-opening do not keep 

 step with those other modifications of its position. The consequence is a 

 series of varied combinations, which may be of considerable utility in the 

 diagnoses of genera. They also enable the beaks of species to be placed 

 in developmental position in regard to one another, and, if there is incon- 

 gruity, suspicion may usefully be aroused as to whether a species is rightly 

 placed, suggesting investigation of its internal details. 



For instance, the beak of Bouchardia is, in regard to position of foramen, 

 just attaining to the epithyrid stage — perhaps something of the permeso- 



5* 



