316 RHYNCHONELLIDA. 
Shell like that of Rhynchonella; the lower half of the ventral 
valve with a broad, deep sinus. V aly es articulating by means of 
two teéth in the ventra valve, with corresponding sockets in the 
dorsal valve,and a median septum embraced between the deeply 
bifurcating cardinal process of the opposite one. 
Dorsal valve with four crural processes; in the ventral valve 
the dental plates are represented by elevated lamellz surrounding 
the muscular impression, which is much stronger and differs in 
some respects from that of Rhynchonella. 
DiMERELLA, Zittel, 1870. 
Syn.—Cryptopora, Jeflreys, 1869. Atretia, Jeffreys, 1876. 
Distr.—Recent. D. gnomon, Jeffreys. Europe. Fossil; 
Triassic. 
Shell small, Rhynchonelloid, impunctate, with a large fora- 
men; neural valve with an entire edge without a septum ; hemal 
valve with a large, very prominent septum, which divides the 
cavity of the shell, when closed, into two chambers; with two 
stout, diverging hook-shaped crura as in Rhynchonella. 
RHYNCHONELLINA, Gemellaro, 1871. 
Distr.—4 sp. Jurassic; Sicily. &. Suesst, Gemm. 
Shell quadrangular or triangular, smooth or radially ribbed, 
hinge-margin nearly straight; large valve swollen, with curved 
beak, a large triangular area, with a rudimentary deltidium and 
oval opening; teeth and pits as in Rhynchonella; upper valve 
less swollen or flattish, with two very long crura, almost reaching 
the opposite valve, these crura sometimes provided, near the 
hinge, with sickle-shaped processes. 
STrRICKLANDINIA, Billings, 1863. 
Etym.—Dedicated to the late Professor H. E. Strickland. 
Syn.—Stricklandia, Billings, 1859 (non Buckman). TRens- 
seleeria (pars), Hall, 1859. 
Distr.—10 sp. Silurian; N. America, England.  S. elongata, 
Vanuxem, is the only aoe known in the Devonian rocks. 8. 
lens, Billings (cxxxvi, 81). 
Shell usually large, rie ella etc.: valves nearly equal, 
never globose; a short mesial septum in the interior of the 
ventral valve supporting a small triangular chamber beneath 
the beak as in Pentamerus; in the dorsal valve no longitudinal 
septa, spires, or loop, the whole of the internal solid organs 
consisting of two short or rudimentary dental plates, which in 
some species bear prolonged calcified processes for the support 
of the cirrated arms. _A more or less developed area in the 
ventral valve. 
In S. /evis and S. microcamerus the hinge-line is straight and 
much extended. In S. Arachne, Billings, the area of the ventral 
