THE CAEBONIFEROTJS fOEMATIONS OF THE BRITISH ISLES. 507 



2. Phreatura *, gen. no v. 



Valves small, subreniform in outline ; seen from above or below 

 the carapace is subcuneiform, pointed in front, truncate behind. 

 Left valve the largest, and overlapping the other nearly all round. 

 The surface of the valves smooth, but impressed at each end with a 

 comparatively large and deep pit ; hence the name. The only species 

 yet known, namely, Phreatura concinna, J. & K., is about ^^^ inch 

 long, and is very neat in shape. This genus approaches the Silurian 

 Thlijpsura. 



3. YouNGiA, gen. nov. 



Minute, elongate, subrectangular, thick-sheUed, and smooth, with 

 a straight dorsal border that has the contact- surface of the hinge- 

 margin denticulated along its whole length, after the manner oiArca. 



Only one species {Y. rectidorsalis, J. & K.) of this genus is as yet 

 known to us, and it was discovered by our friend Mr. John Young, of 

 Glasgow, with whose name we associate the genus. The discovery of 

 additional species may probably add to the generic characters. The 

 chief feature of the genus, as now known to us, is its toothed 

 hingement, which is certainly unique among the Carboniferous 

 Entomostraca, though partially represented in Gytheridea among 

 later forms. 



Note. — Since this paper was read many of the species here men- 

 tioned have been described and figured in the Annals & Mag. Nat. 

 Hist, for October 1886, and the Geological Magazine of the same 

 date. Others in the Proceedings of the Geologists' Association, 

 vol. ix. part 7. With them also the following new species have been 

 described and have to be added to the following lists and Table, 

 namely : — 



Cythere ? ohtusa, J. & K. Yoredale series ; Lowick, Northum- 

 berland. Ann. & Mag. Nat. Hist. October, 1886, p. 266, pi. ix. 



Beyrichiojpsis cornuta, J. & K. Carboniferous Limestone series ; 

 Linlithgowshire, Pifeshire, and Northumberland. Geol. Mag. Oct. 

 1886, p. 436, pi. xi. fig. 11. 



Beyrichiella cristata, J. & K. Calciferous Sandstone series ; Ean- 

 derstone, Fife. Geol. Mag. Oct. 1886, p. 438, pi. xii. fig. 6. 



We may add that Cythere ? cuneola, corniyera, pyrula, and thraso 

 are now referred to Bytliocypris with some doubt ; and C. ? luaata 

 more decidedly to that genus. Beyrichia Holliana may be a Pri- 

 onitia ; and B. reticosa and ventricornis probably belong to Bey- 

 richiella. Bairdia subcylindrica? (Miinster) should have been 

 entered under sp. 146 as belonging to the Lower Carboniferous of 

 East Scotland (p. 500). 



* From 0peap(-aros), a well or pit, and oupa, a tail. 



