WOODWARD HIPPURITIDiE.
53
The CaprinellcB have been described, and some new species figured,
by Mr. D. Sharpe*, in his memoir "On the Secondary Rocks of
Portugal f." I am disposed to agree with Mr. Sharpe in combining
D'Orbigny's genera Caprinella and Caprinula ; but there does not
appear to have been so many and such regular "water-chambers"
in the spiral valve of Caprinula as in that of Caprinella.
Figs. 28, 29. — Internal ca5^5 q/" Diceras and Requienia.
Fig. 28. Fig. 29.
Fig. 28. Diceras arietinum. \. Fig. 29. Requienia Lonsdalei. ^.
a, point of attachment ; c, c, c\ casts of dental pits ; t, /, t, t', t\ fur-
rows produced by muscular ridges.
Requienia. — A still further connecting link between the Hippu-
rite and ordinary bivalves is supplied by the genus Requienia (Ma-
theron), of which one species, well known as the Diceras Lonsdalei,
is found in the Neocomian of Wilts and Spain. M. D'Orbigny has
merged Requienia in Caprotina in his latest publication (Cours ele-
mentaire Paleont.), placing it amongst the Palliobranchiata ; whilst
Mr. Sharpe regards it as at best only a subdivision of Diceras.
Eight species of Requienia are known, ranging from the Neoco-
mian to the Chalk, and found in France, Spain, England, and lately
in Texas by Dr. F. Roemer. They are attached by the left valve,
the right being usually much smaller, and sometimes round and con-
cave, as in R. ammonia, Goldf. (fig. 31). The interior, however deep
and spiral, is not camerated ; the hinge, as indicated by casts, must
have resembled that of Diceras.
The HippuritidcB and their Geological Distribution. — Excluding
Requienia, there are four genera, — Caprotina, Caprina, Caprinella,

• The CaprinellcE are described by Mr. Sharpe as *' probably attached when
  

young by the spiral valve," which is contrary to analogy, and opposed to the ob-
servations of M. D'Orbigny. Mr. Sharpe also regards the ligamental furrow as
indicative of an external ligament ; whilst it is unquestionably a mere inflection
of the shell-wall, leading to the cavity of the internal cartilage. In the same
description, the oblique plate which divides the umbonal cavity of the straight
valve is confounded with the transverse septa which form the water-chambers ;
whereas it corresponds to the posterior " adductor-inflection " of Hippurites, Ca-
protina, and Diceras.