382 MOLLUSCA. 
Inhabits the Island of Mangsi, Sooloo Sea, 
Differs from other similar species in having regularly disposed, 
rather distant raised lines, with intervening smaller ones, instead of 
having them all of uniform size, as in C. equestris and C. lthedaphus, 
to which latter it is closely allied. 
Figures 488, 488 a, 488 6, exterior, interior, and lateral views of the 
shell; 488, details of sculpture, magnified. 
PILEOPSIS CRYSTALLINA (Gould). 
Testa parva, candida, crystallina, nitidissima, semiglobosa, ad basim 
ovata, sulcis profundis creberrimis radiantibus acutis insculpta ; apice 
terminali, acuto, vix torto, submarginali: margo anticé acuminatus, 
posticé septiformis. 
Pileopsis crystallina, Goutp; Proceed. Boston Soc. Nat. Hist., il. 
161. August 1846. Expedition Shells, 16. 
SHELL small, white, crystalline, shining, ovate at base, dome-shaped, 
with the apex terminal, acute, and slightly curved, projecting beyond 
the margin, which it closely approaches. The surface is very deeply 
furrowed with narrow, radiating lines, thus leaving narrow, abruptly 
raised ribs, which are somewhat undulated by the stages of growth. 
The interior is glassy, especially near the margin ; which is anteriorly 
thinned down to a very sharp edge, and which posteriorly is flattened, 
and projects over the cavity, like the septum of a Crepidula. Mus- 
cular impression faintly marked. 
Length half an inch; breadth three-eighths of an inch; height one- 
fourth of an inch. 
The beautiful crystalline, quartz-like lustre of this shell, its deep 
and regular sulci, and its crepiduloid base, mark this species very 
distinctly. 
Its locality is doubtful, but its perfection shows that it came from a 
coral region. 

