r 



THE CRETACEOUS FORMATION. 13 



A somewhat allied species, having two projections or bosses on each valve, instead 

 of one only, occurs in the Forest-marble. 



No. 4. Cythere Faba, Bcuss. Tab. II, fig. 4 a—c. 



Ci-THEEiNA Faba, Uems. Verstein. Bohm. Kreidf. p. 104, n. 9, pi. xxiv, fig. 13. 



INCH. 



Length, Jg- Detritus, Cbaring. 



Height, jV 



Thickness, -V Chalk-marl, Bohemia (Reuss). 



Carapace irregular oblong, somewhat bean-shaped ; anterior half narrower than the 

 posterior. Dorsal border elliptical ; ventral incurved at its anterior third ; anterior 

 extremity obliquely rounded ; posterior subacute. 



Dorsal asjject compressed oval ; anterior oval. 



This species (of which we have but one specimen) appears to be identical with 

 C. Faba, Reuss, described by him as found in the Planermergel of Bohemia. In the 

 Upper Oolite there is a Cythere, occurring in great numbers, which in its young state 

 is like the species under notice, but when adult, is somewhat elongated and incurved 

 on the dorsal and ventral margins, not unlike var. piriformis of C. amygdaloides, 

 Cornuel (Ent. foss. &c., pi. 8, fig. 11). 



No. 5. Cythere Bairdiana, nobis. Tab. II, fig. 5 a — c. 



INCH. 



Length, ^U Greensand, Farringdon. 



Height, J, 

 Thickness, \-^ 



Carapace-valve (right) somewhat triangular, convex, obliquely rounded anteriorly ; 

 ^wb&.Q,Vit& posteriorly ; Tpunctated ; ptmctations coarse, arranged somewhat longitudinally; 

 Dorsal margin somewhat produced at the anterior hinge ; ventral margin slightly in- 

 curved. Anterior hinge provided with a prominent, oblong tooth, with a cavity on the 

 inside at its base. Tlie valve in profile nearly straight, rather less gibbous at the 

 anterior than at the posterior extremity. A single valve, with its characters some- 

 what obscured by crystallization, was the only specimen found ; it closely approaches 

 C. iM<//m, Miinster, (Jalirbuch 1838, p. 516, n. 6, pi. vi, fig. 6,) but is very much 

 smaller, more obtuse posteriorly, and differs materially in the character of its anterior 

 hinge, having a prominent hinge-tooth, which is obsolete in C. Miilleri, and a large oval 

 tooth-socket, which in C. Miilleri is long and narrow. 



This species we have named in compliment to Dr. Baird, who has so greatly 

 enriched the sciences of Zoology and Comparative Anatomy by his researches in the 

 natural history of Entomostraca, &c. 



