BRACinOPODA. 77 



edge, one on either side of tlie niedi;in line ; a second, smaller pair, placed 

 directly beloAV the former ; and ontside of the latter a third pair of large elon- 

 gate or subreniform impressions, converging forward. Beneath the rostrnm 

 there is a prominent spoon-shaped pit or chamljer separating the above men- 

 tioned impressions, with which the groove of the area is conliiient. In the 

 dorsal valve there are also three pairs of impressions disposed in nearly the 

 same manner with those of the ventral valve. The dorsal valve is not known 

 to possess an area. The surface is concentrically striated." 



From the specimens before us, the shell-sul)stance ol' Elkania desiderata 

 appears to be largely corneous and distinctly laminated. Several examples in 

 which the external layer of the shell has been exfoliated are covered with 

 conspicuous papillae which may indicate a punctate structure in the iinier layers, 

 a feature not hitherto noticed in Oboi.ella or its immediate allies. We have 

 not been able to discover the minute cardinal area mentioned by Fouo, although 

 this feature should have been retained on tlie specimens examined, if it was 

 distinctly developed. On tlie contrary, there appears to be, just within the 

 marginal apex of what is above considered as the ventral valve, a broad, 

 subtriangular depression, into which the central "spoon-shaped" cavity merges. 

 This central cavity, in five examples of the interior of this valve, has a more 

 or less distinct development, its definition being sometimes obscured by the 

 flattening of the shell. When best preserved, it shows two narrow furrows 

 diverging from its anterior extremity, which continue a short distance and be- 

 come abruptly extinct. These two furrows separate the anterior extremities 

 of the broad lateral muscular scars, which are quite indistinctly limited, while 

 the smaller impressions, termed by Fokd the " centrals", are faint, but dis- 

 tinctly seen in favorable light. The two small grooves in the rostral portion 

 of the shell, diverging from the beak, were regarded by Ford as constituting 

 the " cardinal" scars. These are, however, very elongate, and pass from near 

 the pedicle-groove outward, skirting the posterior portion of the lateral impres- 

 sions, and appear to terminate in distinct, subcircular scars situated between the 

 laterals and the lateral margins of the valve. Should this character prove of 

 permanent value, it will be of significance as aiTording an analogy between 

 Elkania, Obolus and the Trimerellids. 



