356 MAZATLAN UNIVALVES 
407. ?Isapis ————, sp. ind. 
Tablet 1703 contains a fragment of a species resembling 
I. ovoidea, but with very numerous fine spiral ribs, with broad 
concave interstices, crossed by transverse ridges most develop- 
ed on the penultimate whirl. 
Hab.— Mazatlan: 1 sp. on Spondylus ; L’pool Col. 
Famity RISSOIDA. 
Genus RISSOINA, D’Orb. 
Voy. Am. Mer. 1840, p. 395.—Phil. Handb. Conch. p. 172.= 
H, &§& A. Ad. Gen. vol. i. p. 327.—Base slightly channeled, 
labrum thickened, operculum neritoid. 
Rissoa, pars, auct. 
408. Rissorna stricta, Mke. 
R. t. alba, subturritd, solidd, anfractibus ?x., apice ?..... ; 
labro incrassato, ad mediqm partem producto; labio parvo, 
reflexo ; columella truncatd ; costis radiantibus subrotundatis, 
in anfractu utroque circiter xx., striulis spiralibus obsoletis ; 
suturd impressd, costis ad apicem continuis. 
Rissoa stricta, Mke. in Zeit. f. Mal. 1850, p. 177, no. 37. 
Comp. Rissoa fortis, C. B. Ad. Pan. Shells, pp. 178, 314, no. 245. 
Comp. Rissoina pyramidata, A. Ad. 
A single specimen of this shell was found by Mr. Hanley in 
the Spondylus washings. Menke’s shell is still larger, measur- 
ing 3°7 by 1° lines. Even Mr. Hanley’s specimen is very 
much larger than R. Woodwardii, which in general form it 
much resembles, measuring long. °27, long. spir. (apice carente) 
aif tat. oll, daze. 20°. 
Hab.—Mazatlan ; extremely rare ; Havre Col. 
Tablet 1704 contains some fragments which seem to belong 
to this species, with an apex resembling that of R. Woodwardii, 
but larger in proportion; and a sketch of the unique shell in 
Mr. Hanley’s Collection. 
