222 Prof. T. R. Jones and Dr. H. B. Holl on 



3. Primitia excavata^ sp. nov. PI. XV. figs. 10 a^ 10 J, 10 c. 



Valves siiborbicular, nearly semicircular on the ventral edge, 

 straight on the short dorsal margin, with nearly equal angles 

 for the well-marked anterior and posterior slopes. This out- 

 line is exaggerated in contrast with that of the somewhat Le- 

 perditioid Primitia jpusilla^ J. & H., Ann. Nat. Hist. ser. 3. 

 vol. xvi. pi. 13. fig. 11, but is essentially similar. The faint 

 dorsal sulcus of the latter, also, is represented here by an oblique 

 antero-dorsal pit, deep and narrow, with a raised anterior 

 border ; and the flattish smooth surface (A P. ])usilla is replaced 

 by an excavated area, broadly semicircular, sculptured with a 

 reticulation of irregular hexagonal pattern. The broad raised 

 margin of this area is longitudinally striated (fig. 10 c), and 

 slopes down suddenly outside to the edge of the valve (fig. 10 a). 



This species is from the Woolhope Limestone, west of the 

 Wych, near Malvern, but is very rare, our specimen being 

 unique. 



Primitia excavata has its valves depressed, like those of 

 Kirkhya and Moorea ; but it has neither the outline of the 

 former nor its definite ridges ; and it differs from the latter 

 in the presence of a dorsal or subcentral pit, and in the absence 

 of a definite marginal ridge. It more resembles such a Pri- 

 mitia as P. pus ilia (above mentioned), with a surface not only 

 depressed but excavated ; and, indeed, unless we were to make 

 a j)rovisional genus for its reception^ it is near this form that we 

 must place it. 



LIST OF THE KNOWN PEIMITI^. 



U^pjy&r- Silurian Primitia. 



Primitia Beyricliiana, Jones Sf Holl, Ann. N. H. s. 3. xvi. 422. Wenlock ; 

 Sweden. 



concinna, Jones, ibid. xvi. 424. Wenlock ; Gothland, Dudley, and 



Nova Scotia : Trenton ; Canada. 



consobriua, Barrande, MS., Thes. Sil. 200. Stage F. f. 2 (Upper Si- 

 lurian) ; Konieprus, Boliemia. 



cristata, /. 4" H. An. N. H. s. 3. xvi. 420. Wenlock ; Malvern. 



excavata, J. S;- H. (in the present paper). Woolhope ; Malvern. 



lenticularis, J. 4'- H. (in the present paper). Woolhope ; Malvern. 



mundula, Jones, An. N. H. s. 3. xvi. 419. Wenlock ; Sweden and 



Malvern. 



muta, J. 4' H. ibid. xvi. 425. Wenlock ; Beechey Island. 



oblonga, /. ^- IL ibid. xvi. 423. Wenlock ; Sweden. 



obaoleta, J. &; II. ibid. xvi. 423. Wenlock ; Sweden. 



ovata, J. Si' II. ibid. xvi. 423. Ludlow ; Abberley and Kington : 



Wenlock ; Sweden. 



pusilla, J. Sf II. ibid. xvi. 424. Wenlock ; Malvern*. 



• This is from the Upper, and not from the Lower Silurian, as stated 

 iundvortontly, Ann. Nat. Hist. ser. 3. vol. xvi. p. 416. 



