Davidson — Earliest British Brachiopoda, 309 



of the valves of 0. desiderata being the only one I have been able to 



examine, and of which I here append ^^ 



a figure. The interior of 0. polita will^^M ^^^^^||^. 2 



be found figured in the 16th Annual ^^^ .^KraBi:^^™^. 



Eeport of the Eegents of the University 



of the State of New York for 1863, and 



some complete illustrations of both 



valves of O. Sagittalis are here given. 



Having sent drawings of these last to 



Mr. Billings, he wrote back, ''Your 



figures show the four muscular scars 



of Ololella, but their proportions are 



quite different from those of 0. chro- 



matica, 0. desiderata, and 0. polita. In 



TTalTq ficmrps? of O 'nnliin tTiP mimonlar 1- Exterior of OJ. (^es/rfemfo, nat. size. 

 Haii S ngures OI U. poma, me muscuiar ^^ internal cast of the same greatly 



scars agree with those of my species as magnified. 

 nearly as two forms of the same genus usually do, but the two an- 

 terior scars are vastly larger in proportion to the size of the shell, 

 than they are in 0. SagittaUs.'' I cannot, however, find any hinge 

 area in the last-named shell, nor groove for the passage of a pedicle, 

 this being visible only so far as I can make it out in 0. ? polita. 



Obolella Sagittalis, Salter, M.S. PI. XV. Figs. 17-24. 



Named only in the Eeport of British Association (p. 285), 1865. 



Discina lahiosa, Salter, ditto. ditto. 



Shell small, rarely exceeding two and a half lines in length and 

 breadth; almost circular, rather broader anteriorly, front broadly 

 rounded, beak in the dorsal valve slightly obtusely pointed, posterior 

 margin in the ventral valve nearly straight or slightly indented in 

 the middle. Valves convex, and more or less deeply marked by con- 

 centric lines or ridges of growth. In the interior of the dorsal valve 

 two rather large, irregularly circular, projecting scars {a., PL XV. 

 Fig. 19) are situated close to the posterior margin, and separated by 

 a moderately elevated tongue-shaped ridge which extends to about 

 two-thirds of the length of the valve {e), and on either side, at about 

 half the length of the valve, are two smaller oval- shaped, divari- 

 cating, slightly-prominent scars {h). (In the cast these projections 

 form corresponding depressions, but they vary considerably in their 

 minor details according to age and specimen.) In the interior of the 

 ventral valve, two oval-shaped, obliquely-placed scars, smaller than 

 the corresponding ones in the opposite valve, and more widely 

 separated, lie also close to the posterior margin {a). A little 

 lower down, two rather larger, but very slightly marked, scars may 

 be noticed ; while between the four muscular impressions a project- 

 ing A-shaped ridge, with most elevated portion (o) in the middle, 

 lies between the first-named scars, and leaves in the cast a deepish 

 angular depression which assumes, at first sight, resemblance to an 

 apicial foramen. 



This well-marked species was named by Mr. Salter in 1865, but was 

 not figured or described. It is tolerably abundant under the condition 

 of internal casts, which are sometimes very sharply marked, so that, 



