NOTES ON AN OSTRACOD AND OSTRACODAL LIMESTONE. 245 



several other genera besides Primitia are probably present 

 in the Middle Devonian Limestone of Australia. 



Description. 



Primitia yassensis, sp. no v., Plate IX, figs. 1 — 3. 

 Seen from the side the carapace is elongate-ovate, 

 narrowing anteriorly; dorsal margin nearly straight ; ven- 

 tral margin gently convex, slightly sinuous in the middle; 

 anterior extremity truncately rounded, posterior extremity 

 obliquely rounded at the ventral angle, and with the dorsal 

 angle truncated. The narrow anterior extremity depressed 

 over one-third the length of the valve, and markedly so 

 towards the antero-ventral angle. Surface tumid in the 

 posterior half, with a moderately deep and curved sulcus, 

 extending from the dorsum to two-thirds across the valve 

 and directed slightly backwards. Surface finely reticulate 

 in places, especially near the margins, the structure being 

 best seen on moistening the specimen. Edge view of valve 

 showing the carapace to be pear-shaped in section. 



Measurements. — Length of specimen (left valve) 1*6 mm. 

 Greatest width, 1*08 mm. Depth of valve, '38 mm. 



Affinities. — The present species clearly belongs to the 

 group of which Primitia mundula, Rupert Jones, forms the 

 central type, and which ranges from the Upper Silurian to 

 the Lower Devonian. 



The nearest allied form to the Australian species is 

 Primitia scaphoides, Rupt. Jones, 1 a fossil ostracod from 

 the Lower Devonian of Campbellton, New Brunswick. The 

 sulcus in P. yassensis, however, is not so deeply excavated, 

 and there is no sub-acute ridge bordering the side nearer 

 the anterior extremity. 



Occurrence. — Middle Devonian, from the 'Cavan cutting' 

 on the left branch of the Murrumbidgee River, Portion 65, 



1 Ann. Mag. Nat. Hist., Ser. 6, Vol. in, 1889, p. 337, pi. xvi, fig. 3. 



