462 Dr. J. Allan Thomson — On the Thecidiince, 



The subfamily appeared in the Devonian, 1 attained its maximum 

 development in the Jurassic and Cretaceous, and is still represented 

 by three living species. The genera are founded mainly on the form 

 of the septum. This is simple in Davidsonetta and Thecidella, bears 

 two lateral branches in Lacazella, and four lateral branches in 

 Thecidea and Thecidiopsis. In Thecidiopsis, Eudesella, and Pterophloios 

 there are in addition a number of lateral septa. 



As in the case of the Terebratulidae and Khynchonellidse, the type 

 genus Thecidea 2 is often used in a broad sense practically synonymous 

 with the subfamily. All the recent and Tertiary species have been 

 ascribed either to Thecidea (sensu lato) or to Lacazella. There is, 

 however, as Hedley has recognized, 3 a stock quite distinct from 

 Lacazella which has not yet been named, and for this I now propose : 



Thecidellina, gen. nov. 

 Genotype Thecidium Barretti, Davidson. 



Shell subtrigonal, attached by the back of the beak ; surface 

 smooth or with concentric growth-lines. Hinge-line broad and nearly 

 straight. Ventral valve with a well-marked area, but apparently no 

 deltidium. 4 In the hollow beak there is a small median septum from 

 which two prongs project in front of the hinge-line. Interior of 

 ventral valve granulose. Dorsal valve with the usual type of cardinal 

 process and bridge. Median septum not branched, tapering behind to 

 a sharp point. Brachial lamellae attached to the end of the septum 

 and curving forwards on each side parallel with the margin of the 

 shell to near the front of the septum, when they are reflected back 

 along the sides of the septum. The margin of the valve, the front 

 of the septum, and the bridge are covered with granules. 



Thecidellina differs from Lacazella in the presence of the prongs on 

 the septum of the ventral valve instead of a muscular plate, and in 

 the unbranched septum and simpler lamellae of the dorsal valve. 

 The dorsal valve is very similar to that of the Liassic Thecidella, 

 in which, however, no bridge has been described and the septum is 

 not acicular but broadly rounded. Moreover, a well-defined deltidium 

 is present in tliis genus. 



Thecidellina includes the recent tropical forms T. Barretti, Davidson 

 (Jamaica) and T. maxilla, Hedley (Funafuti and New Hebrides) and 

 a new species described below from the Tertiary (Oamaruian) of New 

 Zealand. The discovery of the last adds additional weight to the 

 argument that the Oamaruian of New Zealand enjoyed a warmer 

 climate than the present, since the two recent species of the genus 

 have a tropical distribution. 



The only other Tertiary member of the Thecidiinse so far found in 

 the Southern Hemisphere is Thecidium australe, Tate, 5 from the 

 Muddy Creek beds, "Victoria. The interior of the dorsal valve of this 



1 Cf. Siemiradzki, Bull. Intern. Acad., 1909, p. 768 {vide Zool. Eecord). 



2 Thecidium, Sowerby, 1824, is a synonym of Thecidea, Defrance, 1822, and 

 is still often erroneously used for Thecidea. 



3 Mem. Austral. Mus., No. 3, pt. viii, p. 510, 1899. 



4 Cf. Hedley, loc. cit. 



5 Trans. Koy. Soc. S. Austral., vol. iii, p. 116, pi. ix, figs. 3a-c, 1880. 



