ISOCAEDIA MEERILLI. 43 



corresponding to the area 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 niui. ; Ijeiglit, 71 mm. ; thickness, 45 mm. 

 Smallest: " 33 mm.; " 2.3 mm. ; " 17i mm. 



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

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

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

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

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



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

 p. 219, PI. ix, fig. 53) corresponds foirly 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 A', Hjjs. S a, b, c. 



Nucleus ohlicfie irigonus, cordiformis, siuinne tionidiis. cvqiiivalvis, inceqidlateralis ; 

 extremitas anterior brevis, angidata, plus miniisve truncate rotundutu ; margo ventris 

 lente arcuatus ; extremitas posterior ah mnhonihus cito planeque declivis et supra 

 angidmn infero-posteriorem truncatus : gibbositas maxima paiilo postmediana, super 

 umbones deorsum et retrorsuni advcrsvs marginem infero-posteriorem decurrens : um- 

 bones prorsum incUnati, subterminales, inflecti, ad apices acutos late separati : regio 

 lunularis excavato-cordata, dilatata, ei Isocardioe cordis Linn, persimilis : linea 

 cardinalis ut in nucleis Isocardice tgpicce solet : promincntiee impressionibus mus- 

 ctdorum (oilcrinrum, pallii linece et foveolarmn supraj acentimn congruentes altce et 

 generi propricc. 



Cast oljliquely triangular, heart-shaped, extremely tumid, equivalve, in- 

 equilateral ; anterior exti-emity short, angulated, more or less truncately 

 rounded ; ventral margin gently arcuated ; posterior extremity rapidly and 

 fiatly 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 



