ISOCAEDIA MERRILLI. 43 



corresponding to the urea marked, lanceolate, limited by rounded margins : 

 umbones ante-mesial, rather prominent, incurved : anterior muscular scar 

 conspicuous, the posterior one not to be distinguished. 

 Four specimens, casts. Dimensions of those figured : — 



Largest: length, 8-t nun. ; height, 71 mm. ; thickness, 45 mm. 

 Smallest: " 3:3 mm. ; " 25 mm. ; " lTJ.mm. 



The specimens seem to belong to a species hitherto unnamed, and to lie 

 of form so peculiar that it cannot be mistaken. Comparison with an internal 

 cast taken for the purpose, in plaster, from CaUista squalida Sow., leaves very 

 little doubt that the species is rightly to be referred to CalUsta, which, with 

 Stoliczka and Zittel, I prefer to consider a subgenus of Cytherea. 



The very brief description of Venus induraia Conrad (Official Report, 

 p. 219, PI. ix, fig. 53) corresponds fairly to these casts, but the figure cannot 

 be recognized as representing them. 



Collections Merrill and Congregational House. 



Locality and Position. — Beirut district ; Turonian. 



Isocardia Merrilli, sp. nov. 



Plate V, figs. 3 a, b, c. 



Nucleus oblique trigonus, cordiformis, summe iumidus, ceguivalvis, inceguilateralis ; 

 extremitas anterior brevis, angulata, plus minusve truncate rotundata ; margo veniris 

 lente arcuatus ; extremitas posterior ah umbonibus cll<> planeque declivis et supra 

 angulum infero-posteriorem trumatus : gibbositas maxima paulo postmediana, super 

 umbones deorsum et retrorsum adversus marginem infero-posteriorem decurrens : um- 

 bones prorsum inclinali, subterminales, inflecti, nil apices acutos late separati : regio 

 lunularis excavato-cordata, dilaiata, ei [socardise cordis Linn, persimilis : linen 

 cardinalis ut in nucleis Tsocardice typicce sold : prominentice impressionibus mus- 

 culorum anteriorum, pallii linece et foveolarum suprajaceniium congruentes alice </ 

 generi proprice. 



Cast obliquely triangular, heart-shaped, extremely tumid, equivalvc. in- 

 equilateral ; anterior extremity short, angulated, more or less truncately 

 rounded; ventral margin gently arcuated; posterior extremity rapidly and 

 tlatly sloping and truncate above the angle formed by the ventral and 

 posterior margins. The greatest gibbosity is a little back of the middle, 

 beginning upon the umbones and extending along them downward and 



