ORTMANN : TERTIARY INVERTEBRATES. 
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either the Veneridce or the Saxicavidce ( Glycimeridcz ). On the other hand, 
the hinge, with the exception of the anterior part, agrees so closely with 
that of the Cardiidce , that, comparing large species of Cardmm, for in- 
stance C. discrepans Bast., C. laqueatiim Corn*., C. sulcatum Lmck., one 
is at once struck by the close resemblance. Indeed, the hinge is identical, 
but for the complete lack of the anterior lateral tooth in Amathusia. 
The hinge has two cardinal teeth in each valve, and one posterior lateral 
tooth ; the lack of the anterior lateral tooth cannot be regarded as a serious 
reason for separating this shell from the Cardiidce, since in this family 
the’ lateral teeth are obsolete in other genera. 
The ligamental plates (nymphae) are very high in Amathusia , and sepa- 
rated from the umbones by a very deep furrow, a condition that is often 
seen in species of Cardium (for instance C. discrepans , see: Hoernes, 1870, 
pi. 24, f. 1, 2), where it is developed almost in the same degree as in 
Amathusia. 
The pallial impression in Amathusia possesses an almost rectangular 
upward curve posteriorly, which can hardly be called a sinus. The same 
character, and even a distinct sinus is found in some Cardiidce, so that 
this character also does not argue against the position with the Cardiidce. 
The most striking characters that distinguish Amathusia from Cardium 
are : ( 1 ) the lack of the anterior lateral tooth, of which no trace is pres- 
ent; (2) the complete absence of radial sculpture of the shell, and the 
lack of crenulations of the lower margin. 
Record of specimens; Mouth of Santa Cruz River (just above high 
tide) ; 2 double, 2 left valves. 
Distribution: Navidad, Chili (Phil.); Jegua quemada, Suprapatagonian 
beds (v. Ih.) (p. 257; on p. 258, v. Ihering says that his specimens are 
from Santa Cruz). 
Fam. VENERIDAd Leach. 
Gen. VENUS L. 
61. Venus difficillis Ortmann. 
PI. XXVIII, Fig-. 1 “A 
1899 V. d. Ortmann, in: Airier. Journ. Sci., v. 8, p. 428. 
Shell thick, oblique, inflated, posteriorly a little narrowed ; apex situ- 
ated in advance of or at %. of the length. Area long, occupying almost 
