JUKES-BEOWNE : SYNOPSIS OF THE VENEBID^. 69 



I hope that palseontolooists -will give heed to the facts above 

 mentioned, and will not continue to record Meretrix from Cretaceous 

 or Tertiary deposits when they only mean some species of ' Cytherea ' 

 in its widest sense, which they cannot determine more pi'ecisely from 

 the external characters. In most cases it would be better to record 

 it as Cailista (?), or else to continue the use of the name Cytherea for 

 indeterminate fossil forms. 



Synonyms: Cytherea, Lao;., 1805; Nympha, Morch, 1853. 



Type, Ve7ius meretrix, Linn. 



Shell oval or trigonal, sub-equilateral, thick, generally smooth, but 

 sometimes concentrically lirate, with a vernicose periostracum and 

 a minute oblique striation on the posterior slope. Neither lunule 

 nor escutcheon is clearly defined. Ligament rather short and very 

 prominent on strong elevated nymphs. Hinge-plate thick, with 

 three separate cardinals in each valve diverging from a point beneath 

 the umbo ; left posterior confluent with the nymph, right posterior 

 narrow and superficially grooved, others entire. Lateral teeth strong. 

 Both nymphs are corrugated. Ventral margins smooth. Pallial line 

 with a small and shallow sinus. Pedal scar confluent with that of 

 adductor. 



The species are not very numerous, as most of those which have 

 received distinctive names are only colour varieties of M. meretrix, 

 but I should recognize the following as distinct species — peleihialis. 

 Lam., lusoria, Cliem. {=/or}nosa, Sow.), lamarcki, Hanley, lyrata, 

 Sow., and exdis, Desh. 



Genus TivELA, Link, 1807. 



Synonyms: Trigona, Megerle, 1811 ; Trigonella, Conrad, 1837. 



Sliell trigonal, sub-equilateral, solid, smooth, with a more or less 

 deciduous periostracum. Lunule lonj:, but faintly circumscribed. 

 Escutcheon not define<i. 1-igatnent very sliort, prominent, based on 

 thick nymphal plates. Cardinal part of the hinge short and triangular, 

 anterior part elongated. Cardinal teeth 3-3, all narrow and entire, 

 except the left median, which is sometimes grooved ; the left anterior 

 points to the elongate anterior lateral, and the right anterior is close 

 to the lunular margin. Nymphs strongly corrugated, and sometimes 

 divided into a series of ridges which occupy part of the hinge-plate, 

 and simulate supplementary teeth. Dorsal margins grooved as in 

 Cailista, etc. Ventral margins smooth. Pedal scar very long and 

 confluent with that of the adductor. 



Tivela, s.s. Type, Venus corhicida, Gmel.(=F'. mactroides, Born). 



Ventral margins smooth. 



Eiitivela, Dall, 1891. Type, T. perplexa, Stearns. 



Ventral margins crenulated. Only known from Brazil. 



Sub-genus. 



Grateloupia, Desmoulins, 1828. Type, Bonax irregularis, Bast. 

 Synonym : Ci/theriopsis, Conrad, 1833. 



Shell like Tivela, but with a number of oblique parallel ridges on 

 the nymphs, and sometimes a thickening on the posterior dorsal 



