300 Proceedings of the Royal Society of Victoria. 



Observations. — This species was figured by Professor Jones 

 from examples obtained from the Upper Ordovician (Stauro- 

 cephalus Limestone series) of the Lake District, N. of England. 

 Both smooth and punctate forms are nearly isomorphous with 

 Primitia minuta, Eichwald sp. Our specimen is intermediate 

 in character between the typical smooth forms, which it re- 

 sembles in outline, and the punctate variety, which it also 

 simulates in surface ornament. The present examples seem 

 to emphasise the fact of the variability of this species, and to 

 render the separation of the variety as a distinct species from 

 the typical form, for the present, unnecessary.^ 



Locality and Horizon. — Cave Hill, Lilydale. Silurian (Yerin- 

 gian). 



Genus Primitia^ Jones and Holl. 



Primitia trigonaiis, Jones and Holl. (Plate XV., Figs. 8a-c). 



Primitia trigonalis, Jones and Holl, 1865. Ann. Mag. Nat. 

 Hist., ser. 3, vol., xvi., p. 421, pi. xiii., figs. 4 a, b. 



Observations. — The English specimens came from the Wen- 

 lock Limestone of Malvern. I have referred the example be- 

 fore me to the above species, with at first some hesitation on 

 account of the somewhat elongate carapace, but taking into 

 consideration the general thickness of the carapace and the 

 sti'ong compression of the valve edges, it may provisionally 

 be referred to P. trigonalis. It differs from the following 

 species, P. subtrigonalis, sp. nov., in its greater relative thick- 

 ness and compressed margins, and also in the greater angularity 

 in its lateral outline. Our example of the above form carries 

 a series of minute denticules on the posterior edge and on the 

 antero-dorsal angle of the valves. 



Locality and Horizon. ^ — Cave Hill, Lilydale. Silurian (Yerin- 

 gian). 



1 Prof. Jones remarks (ioc. <•)'<.) on the Lake District specimens as follows: — "Figs. 7, 

 8 appear to be varieties of one form ; although possibly if we had better material to study 

 they might be found to be quite distinct." 



