203 
oblong a, dorso elevatd, convexa, albida, fusco pallide variegatd, 
lineis elevatis striisque concentricis obsolete decussatd, antice 
august a, productd , la ter Urns planulatis, extr emit ate posticd ro¬ 
tund at a ^ elevatd ; margine valde sinuatd; foramen perlongum , 
triangidare, postice dilatatum. 
Hab. in littoribus Australise. (Mus. Cuming.) 
8. Macrochisma angustata, A. Adams. M. testa august d, 
oblongd, dorso elevatd , utrinque rotundatd, albida , lineis fuscis 
maculisque rufo-fuscis pictd et tessellatd, costellis obtusis sub- 
rugosis, lineisque depressis, concentricis, subdistantibus, sculptd„ 
extremitate posticd elevatd, margine sinuato; foramen mag¬ 
num, elongatum, subtriangulare, postice dilatatum, excava- 
tum. 
Bab . _ ? 
3. A Monograph of Modulus, a genus of Gasteropodous 
Mollusca, of the family Littorinidje. By Arthur 
Adams, R.N., F.L.S. 
Modulus, Gray. 
Animal with the head proboscidiform, the tentacles tapering, with 
the eyes near their distal ends. Foot small, the sides simple, without 
lobes or filaments. Operculum thin, horny, orbicular, paucispirah 
Shell globose or conical, whorls nodulous; aperture round, or qua¬ 
drangular, not pearly within ; columella anteriorly with a prominent 
lamellitorm tooth ; umbilicus more or less open. 
Modulus, Gray. —Turbo, sp. Adanson-— Monodonta, sp. Lamck.— 
Monodonta, Swains. —Morulus, Reeve. 
The aperture of the shell not being pearly within, and the animal 
being destitute of eye-peduncles, head- and foot-lobes or filaments, at 
once distinguishes this genus from Monodonta, and removes it from 
the family Trochidce. 
1. Modulus lenticularis, Chemnitz. 
Trochus lenticularis, Chem. Conch. 5. t. 1/1. f. 1665. 
Trochus modulus, Linn. Gmel. 
Hab. Mexico. (Mus. Cuming.) 
2. Modulus tectum, Gmel. 
Trochus tectum, Gmel. p. 3569. no. 16. 
Monodonta retusa, Lamck. Rncyclop. 
Hab. Siquejar, Philippines; H. C. (Mus. Cuming.) 
3. Modulus carchedonicus, Lamck. 
Monodonta carchedonicus, Lamck. Hist. An.s. Vert, tom.vii. p. 33 ; 
Chem. Conch. 10. t. 165. f. 1583, 1584. 
Monodonta Sayii, Nuttall. 
Hab. Atooi, California; Nuttall. (Mus. Cuming.) 
