248 rissoa. 



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 Byssomya 

 in the shell, but differing in the animal. Mytilus rugosus, 

 Gmelin. Hypogjea barbata, Poli. 



RHOMBUS. Montf. (pofxfios, rhombos, 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. 



RICINULA. Lam. (Resembling the seed-vessel of the Ricinus.) 

 Fam. Purpurifera, Lam. Entomostomata, Bl. — Bescr. Sub-ovate, 

 thick, tuberculated ; spire short ; aperture narrow, terminating 

 anteriorly in a short canal ; outer-lip thickened, denticulated 

 within, digitated without ; columellar lip spread over a portion 

 of the body whorl, and granulated. — Obs. This interesting genus 

 is composed of some neat little shells allied to Purpura, from 

 which they are distinguished by the finger-like branching of the 

 outer lip, and the granulations of the columella. Fig. 413, R. 

 Horrida. 



RIGHT. See Dextral. 



RIMULA. Defr. A genus consisting of a minute species of 

 Emarginula, Auct. which has a fissure near the margin, but 

 not reaching it. R. Blainvillii, fig. 243. 



RIMULINA. D'Orbigny. A genus of microscopic Foraminifera. 



RINGICULA. Deshayes. A genus founded on Auricula ringens 

 of Lamarck and several small fossils, resembling in some respects 

 Peclipes of Adanson ; they would belong to Tornatella, were it not 

 for the lips being thickened and marginated, fig. 540, A. ringens. 



EISSOA. Freminville. Fam. Ellipsostomata, Bl. Melaniana, 

 Lam. — Bescr. Oblong, turrited, acuminated ; spire long, con- 

 sisting of numerous whorls ; aperture round or oval, pointed 

 posteriorly, dilated anteriorly ; outer lip slightly thickened, 

 emarginated, operculum horny — Obs. The Rissoae are small 

 white, marine shells, considered by some authors as resembling 



