92 RICINULA. 
proaches, and into which, some species run by imperceptible 
gradations. Fig. 393, 394. 
RAPAN'US. Schum. A genus consisting of species of Pyruta, 
Auct. which are thin, much inflated, with short canals. Fig. 
389, P. papyracea. 
ie aes Montf. A species of madrepore, described as 
a Shell. 
RECTILIN'EAR. (Rectus, right; linea, a line.) In a straight line. 
Ez. The hingé of Byssoarca Noe, fig. 132. 
RECURVED. (Re, back; curvo, to bend.) Turned backwards, 
The term applied to symmetrical, conical shells, is used to ex- 
press that the apex is turned towards the posterior margin, as in 
Emarginula, fig. 241. 
REFLECTED. (Reflecto, to fold back.) Turned, or folded back- 
wards. Ex. The edge of the outer lip in Bulinus, fig. 282, is 
reflected, while that of Cyprea, fig. 445 to 450, is inflected. 
RE’NIFORM. (Ren, a kidney; forma, shape.) Shaped like a 
kidney. Ex. The aperture of Ampullaria, fig. 318. 
RENULINA. Lam. A genus of microscopic Foraminifera. 
RE’OPHAX. Montf. A genus of microscopic Orthocerata. BI. 
RE’PENT. (Repens, creeping.) A term applied to those shells, 
which being attached by the whole length of their shell, give 
the idea of creeping orcrawling. Ex. Vermilia, fig. 7. 
RETI’FERA. Bl. The first family of the order Cervicobranchiata, 
Bl. containing the genus Patella. 
REVERSE, or Smistrat shells. Are those in which the aperture 
is on the left side of the shell, when it is held with the mouth 
downwards, and towards the observer, Ex. Balea, fig. 296. 
Attached bivalves are said to be reversed when the left valve is 
free instead of the right; a circumstance which occurs some- 
times in the genus Chama. 
RHINOCU’RUS. Montf. A genus of microscopic Foraminifera. 
RHIZO’RUS. Montf. A genus described from a microscopic 
shell, appearing to be a cylindrical Bulla. 
RHOMBOIDAL. (fopBoedos, romboeidos.) Having a rhombic 
form, i. e. four sided; two sides meeting at acute, two at obtuse 
angles. Conchologists are not very strict in the application of 
this term ; for, indeed, a perfect rhomboidal figure could not be 
found among all the testaceous productions of the sea. 
RHOMBOIDES. Bl. A genus described as resembling Bys- 
somya, in the shell, but differing in the animal. Mytilus rugosus, 
Gmelin. Hypogeea barbata, Poli. 
RHOM’BUS. Montf. (popuBos, rombos, a rhomb.) A genus con- 
sisting of species of Conus, having a rhomboidal or quadrilateral 
form and a coronated spire. Ex. Conus nocturnus, fig. 459. 
RICIN’ULA. Lam. (Resembling the seed-vessel of the Ricinus.) 
Fam. Purpurifera, Lam. Entomostomata, Bl. Deser. Sub-ovate, 
