TROCHID^. 309 



spin}'^ ; 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. 



ANGARTNA, 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 (Ixxx, 3*7). 



CIRRUS, Sowb. (In part, not Orb. Sccevola, 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 Euomphalus and a Pleurotomaria. 



Laxispira, Gabb. 



Distr. — L. Iumb7-icalis, 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 Vermetidae. 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. — r. irzcarzna^a. Meek (Ixxx, 38). Devon.; Ohio. 



Has been proposed for a Delphinula-like shell with wide 

 umbilicus ; it occurs in the palseozoic 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.] 



Trochus, 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 pja'amidal, with nearly a flat base ; whorls numerous, 

 flat, variously striated ; apertui-e oblique, rhombic, pearly inside; 

 columella twisted, slightly truncated ; outer lip thin. 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 



