6 PROF. T. R. JONES ON SOME PALJSOZOIC OSTRACODA 



terval between the two little knobs representing the generic sulcus). 

 The tubercles are relatively larger than in 1\ cequalis, J. & H,, 

 * A. M. N. H.' ser. 5, vol. xvii. 188G, p. 412, pi. xiv. fig. 11, and the 

 valve differs very much from F. hicortiis, Jones, o^>. cit. 1855, p. 173, 

 pi. vi. fig. 23. 



Prom the Bala beds near Welshpool, North Wales. Collected by 

 Mr. J. Bickerton Morgan, F.G.S., to whom we are indebted for this 

 and other Lower-Silurian (Ordovician) species. 



5. Primitia IJLRicni, sp. nov. (PL IV. figs, la, h, c; et var. 

 figs. 2 & 3.) 



Length. Height, 



mm. mm. 



r Pig. 1 -8 -46 



Size^ 2 -73 -4 



[ 3 -8 -46 



Snboblong, straight above, elliptically curved below ; hinder end 

 semicircular ; front part compressed and narrower, with a nearly 

 straight slope, which makes a blunt antero-ventral angle with the 

 lower edge. A small but well-marked tubercle rises on the posterior 

 quarter ; there is a slight subcentral swelling, with a very faint 

 oblique hollow between it and another but faint tubercle in the 

 a ntero ventral region. The valve has a slight convexity, and the 

 hinder tubercle gives a blunt profile to that end of the valve (fig. 1 c). 

 The surface is ornamented with a minute reticulation, which has 

 elongate meshes, and passes into strise along the ventral region. 



Primitia diversa, J. & H. * Ann. & Mag. JS^at. Hist.' ser. 5, vol. 

 xvii. (1886), p. 412, pi. xiv. fig. 10, may be said to be a relative of 

 the species under notice, but the differences of shax^e and surface 

 are sufficiently distinctive. 



Pig. 2 is a variety of P. Ulriclii. It has the central swelling 

 and two little tubercles ; but the anterior tubercle is higher up 

 than in figs, la, 5,, and the outline of the valve is more Leper- 

 ditioid, -and its convexity is more uniform. Except as to the 

 outline of the valve, this shows a striking analogy to the subrhom- 

 boidal and Upper-Silurian Primitia armata (llichter), described and 

 figured in the ' Geol. Mag.' 1881, p. 341, pi. ix. fig. 11. 



In fig. 3 the central swelling only is visible. Without this fea- 

 ture it would probably pass for some of the forms that have been 

 grouped as " Leperditia {Isocliilina) cylindrical^' Hall ; but with it 

 the 'valve approximites to the Devonian Primitia Dagon (J. M. 

 Clafke), 'Bullet. U.S. Geol. Survey,' no. 10, ]885, p. 29, pi. 2. 

 figs. 5, 6, 7. The species is here named after Mr. E. 0. Ulrich, of 

 Newport, Ky., who, having worked assiduously on the Palaeozoic 

 Entomostraca, has favoured me with much information. 



The specimens, figs. 1-3, given to me by Mr. John Young, 

 P.G.S., of Glasgow, are in a slab of Lower- Silurian bituminous shale 

 (" Utica Slate "), full of the remains of AsapJms canadensis, Chapm., 

 Tr'mrthrus Beclcii, Green, Liiir/ula cvrta, Conrad, and Orthoceras, ^)., 

 brought from Collingwood Oil-springs, Lake Huron, Ontario, by 

 Mr. D. C. Glen, P.G.S., of Glasgow. 



