641 



/-. 



I'l Ml XI HI 1 Hi- l 



iiiui.: hltfht n 7J n. Q '11111. 



Tlif largest valve x-t-n has ;i length uf l.l is 111111. ami a hight of M.'.l mm. 



This s|., related t.. - //./. ainl at lir-t I was incline. I 



to -. later \ariety of that >|.i-cic-.. Itnt, considering tin- L'reat constancy 



which prevails ainmiu' the hundreds uf valves uf > innfn which I have 



. ami the equal constancy e\hil>ited liy >'. nriini-*, it h.< Miuuglit ln'-t tu hold 



them a- ili>tinct. I: i fuiin.l it <litlicult to ileciile to which of the two, tf. rrassi- 



>iinl><in't(<i,t\\i* pre-ent form I tore the greater resemblance. 

 with the tir-t of ti. is smaller, a trifle higher, the flat 



narrower, the emU !>;; equal, with the |>o-U>rior extremity more -tron^ly OH 

 ami the l>a>al outline more proiniixMit in the middle. In an end view the profile is 



triangular ami the ventral ed^e thinner. The most proininent point of the 

 surface al-o i- ni" riur. while the limad liorder. which is SO con-|>icin> 



ire for >>h ,le\elu|,ed. For cumi'ari--on with >'. nni- 



luil 'llji'il. MM' flllll>\\ 



i lofiilHy.- -*i.i -i, near Cat, n sola. 



MIDTKI.I.A I MBONATA, . >/'. 



I'l.N I K XI \ f II.- ... .- 



I. V.) LdiKtli > nun : Inn ili-km-ss o 1 mm. 



0.65 " " 0.23 " 



Valve- ovate, slightly oblique, c-mls sulieqiial. dorsuni unilionato. projecting 

 con.-ideralily aliove the straight hin^e line: free margin with a border, narrower 

 ami less distinct on the le; than on the ri^ht; greatest convexity near the 



middle of tl .'d, the point occasionally marked hy a very faint depre^j Mn O r 



disc.. |K)t. 



This almmlant spo than N. has more nearly equal 



ends, narrower and hetter defined t>order. and more uniformly coim join 



the much larger S. ./'/// it dillers too ohvionsly to rpquire 'uniparison. 



'innln may i 1 l>ut i< much shorter and almost round. 



Formation and locality. -l'|-iT lhir.1 uf ti 



ky. 

 41- 



