Vol. 6^.~] ME. S. S. BUCKMAN ON BEACHIOPOD MOEPHOLOGY. 341 



the pectunculus or opposite multicarinate stage ; but it could not be 

 developed out of a pectuncidus-stage, because of this difference in 

 ribbing. Further, the loop forbids connexion with Cincta ; for 

 though Eudesia when adult has a similar dalliniform loop, jet when 

 young, as in Eudesia furcata, it has an ismeniform loop. Beecher 1 

 calls this form Ismenia furcata ; but it is really a young Eudesia 

 retaining the ismeniform loop into the multicostate stage. So 

 Eudesia, even in extreme youth, has reached a much higher stage 

 of: shell-development than adult Cincta ; but it retains in youth a 

 more primitive loop. 



The multicostate stage — fait is, Eudesia — is arrived at by 

 constant intercalation of additional costse. Elimination of these, 

 for which Flabellothyris is a guide, indicates what the preceding 

 stage would be : namely, a pectunculoid or alternate-multicarinate 

 stage. 



Ismenia jiectuncidoides is the example of this stage : and its loop 

 conforms with that of the young Eudesia. The pectunculoid stage 

 would be about equivalent to the quadricarinate stage, only the 

 former is the stage with alternate carination, the latter with oppo- 

 site carination. 



Prior stages to the pectunculoid — stages passing from unicarination 

 to incipient quinquecarination — may be seen in the fossils figured by 

 Deslongchamps as Megerlea Munieri of the Pullers' Earth 2 ■ and 

 unicarination with suggestion of tricarination in his Ismenia 

 Murchisonce of the Inferior Oolite. 3 But Eudesia had, probably, 

 branched off from Ismenia in Inferior-Oolite times, for Deslong- 

 champs figures a Eudesia-like species as Megerlea Bessina in the 

 Inferior Oolite : this form, however, shows the nodose costae of 

 Flabellothyris} 



As an example of the incipient uniplicate stage Terebratula 

 WhitaJceri, Dav. may be given. It shows that upraising of the 

 anterior margin, which would in time, by tachygenesis, produce 

 the conspicuous dorsal carina of Ismenia Murchisonce. Extreme 

 examples of the uniplicate stage, with a conspicuously-elevated 

 dorsal carina, are Terebratula Etheridgii, Dav. of the Aalenian of 

 Europe, and T. euryptycha, Kitchin, of the Oxfordian of Kutch. 



In the series of stages leading up to Eudesia, through which 

 Eudesia is supposed to have passed, it will be seen that the median 

 dorsal carina remains persistent and undivided ; but, in the making 

 of the Biplicatse, which also start from a uniplicate stage, a different 

 method is pursued : the dorsal carina is medianly depressed by a 

 superimposed dorsal sulcus. Terebratula sella of the Cretaceous 

 shows well how this begins. 



Then there are cases of alternate multicostation which may be 



1 ' Revision of the Families of Loop-bearing Brachiopoda ' Trans. Conn. 

 Acad. vol. ix (1893) pp. 384, 385, &c. & pi. i, fig. E 4. 



2 1874, ' Pal. franc. : Terr. Jur. Brach.' p. 315 & pi. xc. 



3 1885, Ibid. p. 378 & pi. cviii, figs. 4-7. 



4 1872, Ibid. p. 241 & pi. lxiv, figs. 6-8. 



