TROCHIDA. 309 
spiny ; aperture round, pearly; peristome continuous; umbil- 
icus open. Operculum horny, many-whorled. On reefs at low- 
water. 
Animal without head-lobes; sides lobed and cirrated. 
ANGARINA, Bayle. (Delphinulopsis, Wright.) Shell sinistral, 
discoidal, umbilicate, spirally ridged, last whorl crowned with 
spines; aperture rounded, nacreous within, columellar margin 
not nacreous. D. Lesourdi, Wright (1xxx, 37). 
cirrus, Sowb. (In part, not Orb. Sczevola, Gemm.) Shell 
sinistral, conical, widely and deeply umbilicated ; spire conical, 
sharp; whorls crossed by longitudinal, nodulous ribs. Liassic. 
D. nodosa, Sowb. England. Sowerby’s genus Cirrus contained, 
besides the above, a Huomphalus and a Pleurotomaria. 
LAXIsPIRA, Gabb. 
Distr.—L. lumbricalis, Gabb (Ixxix, 14°. Cretaceous; New 
Jersey. 
Shell spiral, dextral, partially unwound and the whorls not in 
contact ; aperture simple, lips thin. 
This group is perhaps more nearly related to Vermetide. At 
first sight it appears not unlike Delphinula laxa, Say, but the 
latter is a fossil (Caprotinid) bivalve. 
[ TROCHONEMA, Salter, 1859. 
Syn.—Trochonemopsis, Meek. 
Distr.— T. tricarinata, Meek (1xxx, 38). Devon.; Ohio. 
Has been proposed for a Delphinula-like shell with wide 
umbilicus; it occurs in the paleozoic formations of Europe 
and North America, and, as in so many other ancient groups, 
embraces a number of widely different forms. Professor Meek 
(MSS.) was disposed to place the genus near Delphinula. | 
Trocuus, Linn. 
Etmy.— Trochus, a hoop. 
Distr.—250 sp. World-wide. Low-water to 15 fathoms ; the 
smaller species range nearly to 100 fathoms. 
Fossil, 360 sp. Devonian—; Europe, North America, Chili. 
Shell pyramidal, with nearly a flat base; whorls numerous, 
flat, variously striated ; aperture oblique, rhombic, pearly inside; 
columella twisted, slightly truncated ; outer lipthin. Operculum 
horny, multispiral. 
Animal with two small or obsolete head-lobes between the 
tentacles ; neck-lappets large; sides ornamented with lobes, and 
3-5 cirri; gill very long, linear; lingual teeth 11, denticulated ; 
uncini 90, diminishing outwards. 
TRocHUS (restricted). Umbilical region excavated, but not 
perforated ; columella spirally twisted above, terminating in a 
