The Invertebrate Fauna of the Uitenhage Series. 47 



Oomia beds in dutch ; the resemblance to T. crassa is indeed very 

 striking, though I have elsewhere stated reasons why these two 

 forms cannot be considered identical.* But T. bcyschlagi is certainly 

 either closely related to T. crassa or illustrates a stage of removal 

 from the normal ancestral costate plan, on some parallel line, quite 

 comparable with that exemplified by the Oomia form. It was 

 probably in consequence of insufficient acquaintance with Trigonia 

 smeci that Miiller failed to recognise the true relationships of this 

 peculiar shell ; the points of similarity to the Uitenhage shell See- 

 bachia bronni (Krauss), to which he called attention, are merely 

 superficial, involving the general outward habit only. Uhligt has 

 expressed the opinion, however, that the grounds for the generic 

 separation of these two forms are hardly convincing ; but he can 

 scarcely have compared the figure showing the dentition of the right 

 valve of Trigonia beyschlagil with Neurnayr's excellent correspond- 

 ing illustration of Seebachia. A glance at these figures proves 

 beyond question that Miiller was right in assigning his shell to the 

 genus Trigonia, and now it is interesting to find the clue to its 

 narrower relationships by a comparison with the Oomia forms, a 

 detailed account of which had not appeared at the time when Miiller 

 wrote. 



Amongst the fossils collected at a locality in the district of Ntandi, 

 35 km. west of Mtshinga, which Miiller considered to indicate a Middle 

 Neocomian horizon, a large Gervillia, apparently identical with 

 G. dentata Krauss, serves as a connecting link to both the Uitenhage 

 and Oomia faunas. There is also a Ptychomya (Ptychomya hauchc- 

 cornei Miill.) which, though distinct from P. complicata (Tate), may 

 possibly be nearly related to it. Trigonia bornJiardti Muller, from 

 the same locality, is only so far comparable with the Uitenhage- 

 Oomia Trigonice, that in common with some of these it exhibits a 

 marked posterior elongation, with absence of sculpture from the area 

 and the posterior part of the flank in the adult shell, in which also 

 the area has ceased to be demarcated from the flank. An Astarte 

 from the Oomia Trigonia-beds compares very closely with the shells 

 from Ntandi described by Miiller under the name Eriphyla stuhl- 

 manni, particularly in the character of the hinge and the very deep 

 lunule, though it differs somewhat in the outline and ornamentation ; 

 Astarte herzogi from the Uitenhage beds also belongs to the same 

 division of the genus. 



* Kitchin (1), p. 121. f Uhlig (3). 



I G. Muller (1), pi. zix., fig. 3. 



Holub and Neumayr (1), pi. ii., fig. 4ft. 



