^r \i;yt. AND ci'or.ocir \r, sruvicv 117 



()(■( itrrrucc. — At^llA I'onM A'i'lox. I |i|icr Miirlhoro. 

 Cnlh'cl idit. — Miii'vliiiid ( IcoloLticiil Survey. 



I'.^'lilDiN n;is !• \ i;i LIS n. sp. 

 IM.iic Wl, l''i<rs. rj-8. 

 J)cscri /ilion. — (';ir;i|i;uT iilmiil 1.0 iiiiii. Iimil;-. jukI nearly or quite 0.5 

 nun. lli^■ll; reniforni, strongly ai'clietl dor.-ally. \i'i'\- ^-li^hlly sinuate or 

 strai,i;lit in the venti'al poi'tion of tlie (nitline. and willi the ends rounded 

 and \rv\ nearly e(|ual. the |i(isteri()r onlline howevei- l)ein,Li' usually a 

 triile (ihli(|ne al)(i\c and the turn iido the hasal line slifi'htly lower than 

 at the fiont end; ])oint of greatest thickness above the middle, the slope 

 tnuaid the ventral edge being flatter than elsewhere; edge view elongate, 

 suhelliptieal. the autei'ior extremity more acute than the ])Osterior, the 

 latter lieiug comparatively blunt. Left valve slightly overlapping the 

 right both above and below, its ventral edge somewhat thickened in the 

 middle and bordered along the anterior and posterior thirds of its extent 

 l)y a shar})ly impressed, thin line. Surface generally appearing ciuite 

 snmoth, but under favorable circumstances very small scattered punctae 

 may be observed. Interior of valves with the marginal ])late well de- 

 veloped and Avidest in front. 



This carapace is relatively higher, has a more arcuate back, and less 

 acute anterior extremity (in edge view) than its associate B. suhaeqiiata. 

 It is distinguished further by the dorsal overlap of the valves and in the 

 greater development of the internal marginal plate. 

 Occurrence. — Aquia Foematiox. Upper Marlboro. 

 Collection. — Maryland Geological Survey. 



Family CYTHERELLIDAE. 



Genus CYTHERELLA Jones. 



Cttheeella maklboeoexsis n. sp. 



Plate XYI, Figs. 9-13. 



Description. — Carapace nearly regularly ovate, the height and length 



about as two is to three; 0.9 or 1.0 mm. in length; ventral portion of 



outline somewhat less convex than the dorsal. Eight valve much larger 



than the left and projecting beyond it all aroimd. Edge view obtusely 



lanceolate, with both extremities blunt, the posterior, the more so, and 



