CYTHEROPTERON. 



203 



and has also been found in dredgings from Spitzbergen and Baffin's Bay. G. 0. Sars 

 notices its occurrence in a fossil state in the Glacial formations of Norway. 



Distribution. Becerit. — Baffin's Bay, Norway, Great Britain, Ireland, Spitzbergen. 



Fossil. — Scotland: in nearly all the Post-tertiary beds. England: Bridlington. 

 Norway and Canada. 



2. Cytheropteron nodosum, Brady. Plate VIII, figs. 12 — 15. 



Cythekopteeon nodosum, Brady. Monog. Rec. Brit. Ostrac, p. 448, 



pi. xxxiv, figs, 31 — 34. 



Carapace of the female (?), seen from the side, subtriangular or subrhomboidal ; 

 greatest height in the middle, equal to two thirds of the length. Anterior margin ob- 

 tusely rounded : posterior obliquely subtruncate ; dorsal margin boldly arched, sloping 

 steeply before and behind ; ventral nearly straight : edge of the alseform process 

 crested and sharp. Outline, seen from above, ovate, widest in the middle, extremities 

 pointed, width equal to more than half the length ; end-view trapezoidal ; height greater 

 than the width, angles acute. Surface less distinctly furrowed than in the preceding 

 species, but having two large, rounded tubercles below the dorsal margin, from each of 

 which there runs a more or less distinct elevated rib towards the ventral margin. 

 Length, ^th of an inch. 



Distribution. Becent. — Britain, Ireland, Gulf of St. Lawrence. 



Jb5S27.— Scotland : Lag Arran, Duntroon, Crinan, Kyles of Bute, Cumbrae, Carts- 

 dyke, Dalmuir, Old Mains, Errol, Drip Bridge. England : Bridlington, Hopton Cliff. 

 Ireland : Woodburn, Portrush. Canada and Norway. 



3. Cytheropteron arcuatum, nov. sp. Plate VIII, figs. 16—18 ; and Plate XIV, figs. 



19—22. 



1868. Cythekopteeon vespeetilio, i5ra</?/. Ann. Mag. N. H., ser. iv, vol. ii, 



p. 33, pi. V, figs. 6, 7. 



Carapace, seen from the side, subsemicircular, highest in the middle ; height equal to 

 nearly three fourths of the length ; anterior extremity rounded ; posterior produced in 

 the middle, but in most cases scarcely beaked ; superior margin very boldly and evenly 

 arched ; inferior very slightly sinuated in the middle, bending upwards behind. Outline, 



