388 



MOLLUSCOIDEA 



PHYIÜM Y 



Numerous, laterally directed, brachial ridges in the ventral valve, with corre- 



sponding divergent grooves in 

 the median region of the dorsal 

 valve. Permian; China and India. 



Oldhamia Waagen (Fig. 572). 

 Differs from Lejotodus in that the 

 ventral valve is sub-hemispherical 

 with the incurved apex covered 

 by a callosity, as in Bellerophon. 

 Permian ; India and China. 



Loczyella Frech. Said to be 



like Leptodus, but without the 



^, ,. . , . . r^ ^^"^ t . . ^. r. brachial rideres. May not be a 



Oldhamm decipiens Waagen. Productus Limestone ; Salt t, ^ • i tt /~i ^ 



Range, East India. A, B, Interior of ventral and dorsal brachlOpod. Upper UarDOni- 



ferous ; Nanking, China. 



valves, respectively (after Waagen). 



Subfamily B. Thecidiinae Dali. 

 Thecidiidae with the brachial markings restricted to the dorsal valves. 



Thecidea Defrance (Thecidium Sowerby) (Fig. 573). Dorsal brachial im- 

 pressions with three pairs of symmetrical lobes, radially directed. Cretaceous. 



Thecidea and the following genera of the subfamily Thecidiinae comprise for the 

 most part small, sometimes extremely minute forms, represented from the Trias to 

 the present day ; the climax of diversity occurred in the Cretaceous. 



Lacazella Munier-Chalmas (Figs. 574, 575). Dorsal brachial impressions 



Fig. 573. 



Thecidea papillata Schloth. Upper 

 Cretaceous ; Ciply, Belgium. A, B, In- 

 terior of ventral and dorsal valves, re- 

 spectively, 2/j (after Woodward). 



Fig. 574. 



Lacazella vertnicularis 

 (Schloth.). Upper Cretaceous ; 

 Maestricht. Dorsal valve, 2/j 

 (after Suess). 



Fig. 575. 



Lacazella tnediter- 

 ranea (Risso). Re- 

 cent. Interior of 

 dorsal valve showing 

 brachia, ^/i (after 

 Woodwaid). 



The two large, dorsal, brachial 



with two or three unequal pairs of lobes, medially directed. Jurassic to 

 Eecent; Europe. 



Thecidiopsis Munier-Chalmas (Fig. 576). 

 impressions each have four pairs of lobes 

 laterally and medially directed. Creta- 

 ceous ; Europe. 



Thecidella Munier-Chalmas. Dorsal 

 brachial impressions simple, anteriorly 

 directed. Jurassic ; Europe. 



Eudesella Munier-Chalmas. Trans- 

 verse Shells in which the dorsal brachial 

 impressions have three pairs of simple lobes antero-laterally directed. Jurassic; 

 Europe. 



Fig. 576. 

 Thecidiopsis digitata(ßo\äii.). Greensand ; Essen 

 on the Rhine. A, Dorsal aspect. B, C, Interior 

 of ventral and dorsal valves, respectively, l/j. 



