Vol. 62.] 



BBACHIOPOD HOMCEJUORPHY. 



439 



the glossothyridoid ancestor of the perforate Terebratulids ; in fact, 

 authors have called it Pygope Aspasia. 1 There is in the Upper 

 Lias an imperforate Terebratula (T. erbaensis, Suess) (PL XLI, 

 fig. 24), so like the imperforate cliphya-foTms that Suess himself 

 at one time called it T. diphya, and it has figured in literature 

 as Pygope erbaensis. Have we here the first and last (the 

 glossothyridoid and pileus or imperforate) stages in the development 

 of a series of forms analogous to Antinomia and Pygope, but of such 

 series no perforate species have yet been found? Or did Terebratula 

 Aspasia develop into T. erbaensis without going through a pro- 

 nounced bifi date stage (sima-stage) ? At any rate, the relation of 

 T. pileus to the perforate and the glossothyridoid forms seems to 

 show that, in spite of their dissimilarity, T. erbaensis may possibly 

 be the more or less remote development of T. Aspasia, connected by 

 a greater or less series of bifidate and perforate forms. 



The geological position of the diphyoids is much removed from 

 that of T. erbaensis and T. Aspasia. Pictet [29] says: — 



• This species [T. janitor s.l. = Pygope\ is generally characteristic of the deposits 

 that lie on the borders of the Jurassic and Cretaceous Periods. It [Pygope] 

 probably somewhat preceded diphyoides [Pygites] ; but is, on the other hand, 

 later than the species with small perforation [Antinomia] ' (p. 164). 



Of these Cretaceo-Jurassic strata and their zonal divisions a good 

 exposition is given by Prof. Hang [22], from which I can adapt 

 the following Table (I) to explain the position and sequence of the 

 diphyoids. 



Table i. — Strata yielding Diphyoids (adapted from E. Haug). 



jNeocomiax. 



V A LANG IN 1 AN. 



ANDIAN. 



Upper. 



Upper Volgian. 



Zone of Hoplites, Boissieri. \ 

 Berriasian. 2 J 



Zone of Hoplites Calisto. 



Koniakau Beds. 3 

 Stramberg Beds. 







Lower. 



Lower Volgian. 



Zone of Perisphinctes contiguus. 

 Zone of Oppelia lithographica. 



Upper Pijihga-Kalk. 

 Lower Diphya^K:<xXk. 



1 This rare species can be added to our British fauna. A specimen was found 

 by the late Edward Wilson, F.G-.S., in the Junction-Bed [Middle Lias], 

 Thorncombe Beacon, near Bridport (Dorset). 



2 Kilian [23] p. 430, says that Berriasian = Lower Valanginian, and should 

 be retained in the Cretaceous System. 



3 Pictet [29] p. 165, says that ' the limestone of Koniakau is identicd with 

 that of Stramberg.' 



