MAZATLAN BIVALVES 143 
zensis) St. Domingo, Lamarck :—W. Indies, Bristol Mus.— 
(A. clathrata) Fossil near Angers, Ménard. e 
Tablet 653 contains 6 very young pairs and 7 pairs of valves, 
extremely young, the smallest measuring °04 by ‘02, greatly 
varying in outline. The teeth are at first very few in number, 
and the internal ridge rather prominent.—654, a young pair 
nestled, in situ, in fra ement of Spondylus ealcifer; also 2 
dried byssal feet. —655, 6 sp. young.—656, 8 adult sp., various 
shapes. Two sp. will also be found in situ on Chama (tablet 44.1.) 
195. Byssoarca soLips, Sow. 
Proc. Zool. Soc. 1833, p. 18.—Miill. Syn. Test. Viv. p. 186. 
Area solida, Rve. Conch. Ic. pl. 16, f. 106.—Hanl. Deser. Cat. 
p. 155, pl. 18, f.54.—B. WM. Cat. D’ Orb. Moll. p. 81, no. 716.— 
C. B. Ad. Pan. Shells, p. 262, no. 423. 
This unpretending species greatly resembles our B. lactea, 
and a similar W. Indian species; but differs from each by 
well marked characters. In this, the ligament is in a very 
narrow rhombus; in B. lactea, ina broad one; in the West 
Indian it fills nearly t] the whole area. In B. solida, the hinge 
teeth are nearly or quite obsolete within the ligament, even in 
young shells; in the ether two species the teeth are in an 
uninterrupted line. The surface also in B. solidais generally 
decussated with concentric tubercles; but this character is 
not constant. Shape either flattened and produced, or short 
and much swollen. EHpidermis brown, thin.  Byssal foot 
extremely thin; ventral margin not perceptibly gaping.— 
A finely grown specimen measures long. °35, lat. °56, alt. °28. 
A swollen sp. ecitiie sia dav Ay | yer ty AI Sh ees 
The largest sp. Sabet it AOS von Od i ee ea: 
Hab—Under stones at Paes Peru, Cuming, D Orbigny.— 
Panama and pees not uncommon under stones near low 
water mark; C. B. Adams.—Mazatlan; not uncommon ; 
*pool Col. 
Tablet 657 contains 5 pairs and 1 valve very young, the 
latter ‘03 across; one pair is strongly decussated.—658, 5 sp. 
scarcely decussated. —659, 3do. flat growth.—660, 3 do. with 
former margins projecting.—661, 3 do. swollen.—662, 3 do. 
very much swollen, umbos distant —663, 3 sp. shewing the 
interior. 
