241 



Associated with Sp. J\'(lrO(Via, \n tlie I)evoni;iu suiKlstoncs of 

 Erere. (Morgan Expedition 18T1.) 



[Dedicated respectfully to ]\[adame Elizabeth C. Agassiz. — C. F. 11.] 



Spirifcra Valenteana, Hartt, sp. nov., Plate VIII, fig. 11. 



Test above medium size, veiitricose, thick, trilobed ia outline and sli^'htly 

 transverse, with the greatest width along the hinge line. 



Ventral valve very convex, most elevated between the beak and the middle. 

 Cardinal angles depressed, with the cardinal margins concave. Beak probably 

 large and curving over a rather constricted area. The margin of the valve is 

 distinctly trilobed, caused by the extension forward of the broad mesial sinus 

 beyond the. general margin of the valve; leaving the cardinal extremity on 

 one side at nearly a right angle, it curves regularly inward for more than one- 

 half the whole length of the valve and one-fifth the width, when it gradually 

 bends outward, forming a shallow reentrant curve before reaching the forward 

 projection of the sinus, around which it extends in an elliptical curve. The 

 distance across, from the center of one reentrant curve to the other, is about 

 twice the length of the prolongation of the sinus beyond the general margin 

 of the valve. Mesial sinus very broad and shallow, regularly rounded in the 

 bottom, and with its margins undefined ; width of sinus nearly one-half the 

 width of the valve, the whole anterior lobe of the valve being occupied by it ; 

 in the cast it is nearly as broad near the beak as at the front. The surface of 

 the valve curves regularly and quite strongly from the beak to the front mar- 

 gin ; from each side it curves rapidly upward for about one-fourth the width, 

 and then descends gradually to form the sinus, which is very slightly and 

 regularly concave. 



The dental plates, as indicated by the moulds, were very high and thick be- 

 hind, thinning out gradually as they advance. They are widely separated, the 

 distance between them being nearly one-third the width of the valve, and they 

 extend forward, parallel with each other, for two-thirds the length of the valve. 



Between the dental plates in the mould are indistinct impressions of muscular 

 markings, consisting of an ovate, slightly depressed space, rounded behind, 

 where it is immediately enclosed by the dental plates, and gradually narrow- 

 ing to a point anteriorly, not extending as far forward as the dental plates. 

 This impression seems, however, too limited to include all the muscular mark- 

 ings of the ventral valve. 



But one specimen of this singular species, a cast of the interior 

 of the ventral valve, has been found, and though peculiar in shape, 

 it appears to belong to the genus Spirifei'a. The test was very 

 heavy, and, including the dental plates, was much thickened by 



BUL. BUP. SOC. NAT. 8CI. (31) .lANUART, 1874. 



