rhomb 
going within tlie rhomb, at its outer faces, two total re- 
flections. It is used to produce a ray circularly polarized, 
which becomes plane-polarized again on being transmitted 
through a second Fresnel 's rhomb. Pectinated rhomb, 
in ciinoids, a hydrospire. 
rhpmbarsenite (rom-bar'se-nit), . [< Gr. 
p6!i/]<>(, rhomb, + E. ameiiite.'] Same as cliin- 
dctile. 
rhombi, . Plural of rhombus. 
rhombic (rom'bik), . [= F. rhoiubique; as 
rhumb + -ie.] 1. Having the figure of a rhomb. 
2. In goal., approaching the form of a rhomb 
or diamond, usually with the angles a little 
rounded. 3. In crystal., often used as an 
equivalent of orthofhombic : as, the rhombic 
pyroxenes (that is, those crystallizing in the 
orthorhombic system). 4. In hot., oval, but 
somewhat angular at the sides Longitudinal- 
ly rhombic, having, as a rhomb, the longer dianu'ttT 
in a postero-anterior direction. Rliombic dodecahe- 
dron, octahedron, etc. See the nouns. Rhombic py- 
roxenes. .See pyroxene. Transversely rhombic, hav- 
ingthe longer diameter of the rhomb across the length of 
the body or organ. 
rhombical (rom'bi-kal), a. [< rJiombic + -at,] 
Same as rhombic. 
rhombicosidodecahedron (rom-bl*ko-si-do*- 
dek-a-he'dron), n. [< Gr. pAfifiof, rhomb, rhom- 
bus, '+ etKoat, twenty, + dudemtopov. a dodeca- 
hedron. Cf. icosidodecahedron."] A solid hav- 
ing sixty-two faces twelve belonging to the 
regular "dodecahedron, twenty to the icosahe- 
dron, and thirty to the semi-regular triacontahe- 
dron. Among the thirteen Archimedean solids there are 
two such solids : one, usually so called, has its dodecahe- 
dral faces pentagonal, its icosahedral faces triangular, and 
its triacontahedral faces square ; while the other has the do- 
decahedral faces decagons, the icosahedral faces hexagons, 
and the triacontahedral faces squares. The latter is com- 
monly called a truncated icosidodecahedron, a misleading 
designation. 
rhombicuboctahedron (rombi-ku-bok-ta-he'- 
dron), n. [< Gr. p6uf)of, rhomb, + avfiof, cube, 
+ oKrdedpov, neut. of oKTaeopoc., eight-sided (see 
octahedron).] A solid having twenty-six faces, 
formed by the surfaces of the coaxial cube, oc- 
tahedron, and rhombic dodecahedron. Among 
the thirteen Archimedean solids there are two such solids : 
one, usually so called, has the cubic and dodecahedral 
faces squares, and the octahedral faces triangles ; while the 
other has the cubic faces octagons, the octahedral faces 
hexagons, and the dodecahedral faces squares. The latter 
is commonly called a truncated cuboctahedron, a mislead- 
ing designation. 
rhonibiform (rom'bi-form), a. [< L. rhombus, 
rhomb, + forma, form .] Shaped like a rhomb ; 
rhombic ; rhomboid. In entam., noting parts which 
are of the same thickness throughout, the horizontal 
section being a rhomb: as, rhombi.form joints of the an- 
tenna;. 
Rhombigena (rom-bij'e-nii), . pi. [XL.] A 
variant of Ithonibof/ena. 
rhombo-atloideus (rom"bo-at-loi'de-us), n.; pi. 
rhombo-atloidei (-1). [< Gr. p6[t/3of, rhomb, + 
NL. atl(as) (see atlas 1 , 3) + -oideus.~] A mus- 
cular slip, occasionally arising from one or two 
lower cervical or upper dorsal spines, and in- 
serted into the transverse process of the atlas. 
Rhombochirus (rom-bo-ki'rus), . [NL. (Gill, 
1863), < Gr.pdfiflof, rhomb, +^/D, hand (with ref. 
to the pectoral fin).] A genus of Echeneididx or 
remoras, differing from Remvra in the structure 
5158 
Rhomboganoidei (rom"bo-ga-noi'de-i), . pi. 
[XL., < Gr. piufiof, rhomb, + XL. (!tiii<n<lri.\ 
An order of fishes: same us (iinnli/uiodi. 
rhombogen (rom'bo-jen), n. [< NL. rliombn- 
iirnim: see nk0M&00WKNM.] The inl'usoriform 
embryo of a nematoid worm : one of the phases 
or stages of a nematoid embryo: distinguished 
from nematogeu. See cut under l>ici/i i/m. 
Rhombogena(rom-boj'e-na), ii.pl. [NL.,neut. 
pi. of rhombogeniis : see rhombogenous.'] Those 
Dieyemida which give rise to iufusoriform em- 
bryos. See cut under Dicyema. 
rhombogenic (rom-bo-jeu'ik), a. [< rliomvu- 
gen-oiis + -.] Same as rhombogenoiix. 
rhombogenous (rom-boj'e-nus), a. [< NL. 
rhombogenus, < Gr. pop/tof, rhomb, + -} evfa, pro- 
ducing: see-<7e.] Producing infusoriform em- 
bryos, as a nematoid worm; having the charac- 
ter of a rhombogen. 
rhombohedral (rom-bo-he'dral), <i. [< rhombo- 
liedroii + -/.] 1. In' geoni., of or pertaining 
to a rhombohedron ; having forms derived from 
the rhombohedron. 2. In crystal., relating to 
a system of forms of which the rhombohedron 
is taken as the type. They are embraced iu the 
rhombohedral division of the hexagonal sys- 
tem. See hexagonal Rhombohedral carbonates, 
the Isomorphous group of thenativecarbonatesof calcium 
(calcite), of magnesium (magnesite), of iron (siderite), of 
manganese (rbodochrosite), of zinc (smithsonite). and the 
intermediate compounds, as the double carbonate of cal- 
cium and magnesium (dolomite), etc. These all crystal- 
lize in rhombohedrons and related forms with closely 
similar angles, the angle of the cleavage rhombohedron 
varying from 106' to 1074'. Rhombohedral tfltarto- 
hediism. See Utartohedrism. 
rhombohedrally (rom-bo-he'dral-i), adv. In a 
rhombohedral form ; as a rhombohedron. 
It Inordenskjolditel crystallizes rhombohedrally with 
a : e = 1 : 0.8221, an 1 is tabular in habit. 
American Naturalist, XXIV. 364. 
rhombohedric (rom-bo-he'drik), a. [< rliom- 
bohedron + -ic.~] Same as riiombohedral. Lom- 
met, Light (trans.), p. 290. 
rhombohedron (rom-bo-he'dron), . [< Gr. ptiji- 
/Jof,rhomb,+ foy>a,base.] In //eoi. and 
crystal., a solid bounded by six rhom- 
bic planes. In crystallography a rhom- 
boheoron is usually regarded as a hemihedral 
form of the double hexagonal pyramid. It may 
be obtuse or acute, according as the terminal 
angle that is, the angle 
overone of the edges which 
meet in the vertex is 
greater or less than 90. 
1 
Rfiombofhinis osteofhir. 
of the pectoral fins, which are short and broad, 
somewhat rhombic in outline, and with flat, 
stiff, partially ossified rays. There is but one species, 
R. osteochir (so named from the bony pectoral rays^ oc- 
curring from the West Indies to Cape Cod. 
rhomboccele (rom'bo-sel), w. [< NL. rhombo- 
ccelia.] Same as rhombocoelia. Wilder, N. Y. 
Med. Jour., March 21, 1885, p. 326. 
rhombocoelia (rom-bo-se'li-a), w.; pi. rhombo- 
coelix (-e). [NL., < Gr. p6/ifiof, rhomb, + noMa, 
cavity: see ctelia.'] The sinus rhomboidalis 
of the myelon: a dilatation of the cavity of 
the spinal cord in the sacral region. This is a 
sort of ventricle, or enlargement of the hollow of the 
primitively tubular spinal cord, observable in many verte- 
brate embryos, representing to some extent the compli- 
cated and persistent system of ventricles in the oppo- 
site end of the same neural axis ; but it is not often well 
marked in adults. It is most notable and persistent in 
birds, in which class it presents the figure which has sug- 
gested the term sinus rhoinboidalis and its later synonym 
rhombocoelia or rhomboccele, applied conformably with a 
recent system of naming the several coelia) of the cerebro- 
spinal axis. See cut under protovertebra. 
rhombocoelian(rom-bo-se'li-an),a. [< rliombo- 
ruitii + -<ui.~\ Pertaining to the rhombocoelia, 
or having its characters. 
Khombohedrons. t, obtuse ; 2, 3, acute. 
rhomboid (rom'boid), a. and H. [= OF. rliom- 
boide, F. rhomboide = Sp. It. romboide = Pg. 
rhomboide, < L.- rkomboides, < Gr. pofijioetoi/f, 
rhomboid-shaped, < bApfioc,, rhomb, -t- fWoc, 
form.] I. . Having a form like or approach- 
ing that of a rhomb; having the shape of a 
rhomboid (see II., 1); rhomboidal. Specifically 
(a) In anal., rhonibiform, as a muscle or ligament; per- 
taining to the rhomboidei or rhoml>oideuni. (b) In bot. , 
imperfectly rhombic with obtuse angles, as some leaves. 
Rhomboid ligament. Same as rhomboideum. Rhom- 
boid muscle. Same as rhomboideus. 
II. . 1. In geom., a quadrilateral figure 
whose opposite sides and angles are equal, but 
which is neither equilateral 
nor equiangular; anon-equi- / 
lateral oblique parallelo- / / 
gram. 2. In crystal, a solid * 
having a rhomboidal form Rhomboid, i. 
with three axes of unequal lengths, two of which 
are at right angles to each other, while the third 
is so inclined as to be perpendicular to one of 
the two axes, and oblique to the other. 3. In 
anat., a rhomboideus. 
rhomboidal (rom-boi'dal), a. [= F. rhomboidal 
= Sp. It. romboidale; as rhomboid + -al."] Hav- 
ing the shape of a rhomboid. 
A rhomb of Iceland spar, a solid bounded by six equal 
and similar rhomboidal surfaces whose sides are parallel. 
Brewnttr, Treatise on Optics, ii. 22. 
Rhomboidal fossa, the fourth ventricle of the brain. 
Rhomboidal porgy. See poryy. Rhomboidal sinus, 
the fourth ventricle. 
rhomboidea, . Plural of rhomboidenm. 
rhomboidei, . Plural of rhomboideus. 
rhomboides (rom-boi'des), . [< L. rhomboi- 
des, < Gr. poufioctdcf, neut. of po/i/}of/i!;/f, rhom- 
boid-shaped: see rhomboid.'} 1. A rhomboid. 
[Kare.] 
Rhopalodinidae 
See them under sail in all tlieir lawn anil sarcenet, with 
a geometrical rhnmli"iilf* "i>ii tln-lr heads. 
Milton, Reformation in Eng., ii. 
2f. [cttp.~\ [NL.] An old genus of fishes. Klein, 
1745. 3. [</<.] [NL.] A genus of mollusks. 
l>c Blninrille, 1824. 
rhomboideum (rom-boi'de-um), n.; pi. rliom- 
hniilca (-a). [NL. : see rhomboid.'] In anat., the 
ligament which unites the sternal end of the 
clavicle with the cartilage of the first rib; the 
rhomboid ligament: so called from its rhombic 
form in man. 
rhomboideus (rom-boi'de-us), .; pi. rhom- 
boidei (-i). [NL. (sc. niiisculiis, muscle): see 
rhomboid.'] Either of two muscles, major and 
minor, which connect the last cervical vertebra 
and several upper dorsal vertebrae with the 
vertebral border of the scapula. Rhomboideus 
OCCipltalls, an additional muscle sometimes found run- 
ning parallel with the rhomboideus minor, from the scap- 
ula to the occipital bone. 
rhomb-solid (romb'sol'id), w. A solid gener- 
ated by the revolution of a rhomb on a diago- 
nal. It consists of two equal right cones joined 
at their bases. 
rhomb-Spar (romb'spar), n. A variety of dolo- 
mite occurring in rhombohedral crystals. 
rhombus (rom'bus), w.; pi. rhombi (-Mi). [L.: 
see rhomb."] 1. SameasrAowfi. 2. [cap.'] An 
obsolete constellation, near the south pole. 3. 
[NL.] Inichth.: (a) [cap.~] A genus of Stroma- 
teidse, generally united with Ktromatcus. La.ce- 
pede, 1800. (6) The Liimcau specific name of 
the turbot (as Pleuroiiectcs rhombus), and later 
[c<y>.] a generic name of the same (as Khom- 
bus maximtts), and of various other flatfishes 
now assigned to different genera. Curicr, 1817. 
rhonchal (rong'kal), . [< rhonclnts + -?.] 
Relating or pertaining to rhonchus Rhonchal 
fremitus, a vibration or thrill felt in palpating the chest- 
wall when there is mucus or other secretion in the bron- 
chial tubes or a cavity. 
rhonchial (rong'ki-al), a. Same as rhonchal. 
rhonchisonant (rong'ki-so-naut), a. [< LL. 
rhonchisoitiis, snorting (said of the rhinoceros), 
< L. rhonclnts, a snoring, snorting, + sonare, 
sound: see sonant.'] Snorting. [Rare.] Imp. 
Diet. 
rhonchus (rong'kus), >/. [= F. rhonciis = Sp. 
Pg. ronco, < L. rhonchus, < Gr. *p6yxf> pfyxC> 
prop, pt) xof , a snoring, snorting, < piyneiv, rarely 
piyx elv , snore, snort.] A rale, usually a bron- 
chial or cavernous rale Cavernous rhonchus, a 
cavernous rale. Cavemulous rhonchus, a small caver- 
nous rale. Rhonchus sibilans, a sibilant rale. Rhon- 
chus soiiorus, a sonorous rale. 
rhone (ron), n. An erroneous spelling of rone 2 . 
rhopalic (ro-pal'ik), a. [= F. rJwpaliqiie, < LL. 
rltopalieus, < Gr. pojra/.ik6f, lit. like a club (in- 
creasing gradually in size from one end to the 
other), < poTra'/ov (> ML. rhoptilitm), a club, < pe- 
mw, incline.] In one. pros., noting a hexame- 
ter in which each succeeding word contains 
one syllable more than that preceding it. Also 
spelled ropalic. 
Rhopalocera (ro-pa-los'e-ra), n.pl. [NL. (Bois- 
duval, 1840), neut. pi. of rho]>aiocenis : see rho- 
palocerous.] One of two suborders of Lepidop- 
tera, characterized by the clubbed or knobbed 
antennae (whence the name); the butterflies, or 
diurnal lepidopterous insects: contrasted with 
Heterocera, the nocturnal lepidopterous insects, 
or moths. In a few exceptional cases the antenna? are 
filiform, pectinate, or otherwise modified. Tin/ wings are 
elevated when at rest, and there is no bristle connecting 
the two wings of the same side. The larva? are very vari- 
able, but are generally not hairy, and never spin cocoons. 
Five families are usually recognized, the Nymphalidx. 
Erycinidje (or Lfmvniidx), Lycsenidse, Pajtilifmidte, and 
Hespertidx. The genera (including synonyms) are 1,100 
or more in number : the species are estimated at 7,000. 
About 460 species inhabit Europe, while about 620 are 
known in America north of Mexico. 
rhopaloceral (ro-pa-los'e-ral), ti. [< rliopalo- 
cer-oits + -al.~\ Same as' 'rliopiilocerotts. 
A wealth of illustration to which rhopatoceral literature 
was hitherto a stranger. Athenaum, No. 3141, p. in. 
rhopalocerous (ro-pa-los'e-rus), a. [< NL. rlio- 
palocents, <Gr. jWiroXov, aclub, + w'pn?, ahom.] 
Having clubbed antennas, as a butterfly; of or 
pertaining to the Rhopalocera, or having their 
characters. 
Bhopalodina (ro"pa-lo-di'im). n. [NL., < Gr. 
poKa/.ov, a club, + '-d- (mea'hingless) + -ina."] 
The only genus of Khojmlwlhiidie. B. lageni- 
f or mis is the only species. J. E. Gray. 1848. 
RhopalodinidaB(r6"pa-lo-din'i-de), n.pl. [NL., 
< Kliopiilodinti + -ills-.'] A family of dioecious 
tetrapneumonous holothurians. represented by 
the genus Hhopalodilta. They have separate sexes, 
four water -lungs or respiratory trees, a lageuiform budy 
