8 JURASSIC BIVALVIA AND GASTROPODA 



In the same year Lange (1917) reverted to the subject of the Tendaguru trigoniid 

 which he had recorded as Trigonia smeei J. de C. Sowerby in 1914. He remarked 

 that this species appeared to be a characteristic fossil of the Tithonian, and also 

 noted that there was some similarity between it and a South American form which 

 Jaworski had described as Trigonia burckhardti. 



Reck (1921) described a small series of molluscs collected along the railway running 

 inland from Dar es Salaam. The specimens came from a section between 139-5 and 

 I 39'75 km. from that town (according to the former alignment of the railway, since 

 changed), that is, a little to the west of Kidugallo station. In addition to several 

 forms identified only generically, the species recorded included a representative of 

 a new genus of Arcticidae (Dietrichia parvula gen. et sp. nov.) and a small gastropod 

 described as Neritodomus subkidugallensis sp. nov. The fossil evidence was not 

 clear enough to enable an exact date to be assigned to this bed, but Reck considered 

 that not only was it the lowest fossiliferous horizon exposed locally, but also that it 

 was the lowest horizon with marine Jurassic fossils which up to then had been found 

 anywhere in East Africa. He considered that it might lie close to the boundary of 

 the Upper Lias and Dogger. In 1924 Hennig published a detailed account of the 

 Jurassic beds, ranging from the Lower Dogger to the Lower Malm in German termino- 

 logy, exposed along and near the same railway, between Kidugallo and Ngerengere. 

 He recorded and in some cases figured a number of bivalve and gastropod species 

 previously known from Europe or elsewhere, and described the following as new : 

 Modiola menzeli [Upper Dogger ; not figured], Ostrea {Alectryonia) bornhardti 

 [Upper Dogger], Isocardia substriata [Callovian], Pteroperna africana [" Lower 

 Malm "], Corbula pseudomucronata [Oxfordian], Anisocardia recki [Oxfordian]. 



Dietrich (1925) gave an account of fossils collected in the Mandawa-Mahokondo 

 area of Tanganyika, where the succession of Upper Jurassic beds is entirely marine 

 and uninterrupted by dinosaur-bearing beds as at Tendaguru. His paper dealt 

 mainly with the cephalopods, but the small number of bivalves recorded included a 

 new species, Gryphaea hennigi, thought to be Kimmeridgian in age. Gregory (1927) 

 placed on record the discovery near Mombasa of a specimen of the species then 

 known as Parallelodon egertonianus (Stoliczka), already discovered in Somaliland 

 and Arabia as well as in the Himalayas, where it occurs typically in the Spiti Shales. 

 Two years later a note by Parsons (1929) recorded the presence of the bivalve 

 Posidonia cf. ornati Quenstedt in the Miritini Shales (Callovian) of the Mombasa 

 district. 



This period was marked by a renewal, on the part of Kitchin (1926, 1929), of the 

 discussion initiated by German workers regarding the age of the dinosaur beds at 

 Tendaguru. Kitchin (1929 : 208), as the result of his work on the Cutch Jurassic 

 bivalves, had concluded erroneously that Trigonia smeei occurs in that area in Lower 

 Cretaceous beds, and was therefore loath to accept the conclusion that the " T. 

 smeei " beds at Tendaguru belonged to the Upper Jurassic, particularly as certain 

 species (Trigonia ventricosa (Krauss), Seebachia bronni (Krauss), Astarte herzogi 

 (Goldfuss) and Gervillia dentata (Krauss)) originally described from the Lower Cre- 

 taceous Uitenhage beds of South Africa had been recorded from them. Ammonites 



