MAZATLAN BIVALVES lil 
inent by the hollowing out of the sides. Long. *025, lat. *035, 
alt. °02. 
Hab.—Mazatlan ; 1 valve off Spondylus ; L’pood Col. 
Tablet 498 contains the specimen. 
158. Lepton DionmvuM, 7. s. 
L. t. papyracea, alba, subtrigonali ; levi, striulis inerementi 
minimis confertissimis : inequilaterali, marginibus dorsalibus 
subrectis ; cardine dent. lat. duobus curtis, prominentibus, fos- 
sam ligamenti haud parvam continentibus. 
_ In the only valve found of this species, there is no cardinal 
tooth. The shape nearly resembles some species of Dione, 
with the dorsal margins nearly straight, and at right angles. 
It is known at once from L. Clementinum by the absence of 
cellular markings and concentric undulations, the place of the 
latter being supplied by minute crowded strie of growth. 
Long. ‘04, lat. °06, alt. °03. 
Hab.—Mazatlan ; 1 valve off Spondylus; Z’pool Col. 
Tablet 499 contains the specimen. 
159. LEPTON UMBONATUM, 12. s.* 
Lt. subquadraté, subinflata, cinerea, opacd; striis incrementi, 
atem huc et illuc liris acutis concentricis ornatéd ; umbonibus par- 
vis, valde prominentibus ; margine ventrali compresso ; cardine 
dent. lat. haud longis, excurvatis ; fossa ligamenti valde depres- 
sa; impress. muse. subrotundatis. 
Shell Kellia-shaped, but with a small extremely prominent 
umbo, and a flattened ventral edge. Surface of a dull ashy 
colour, with an extremely thin epidermis ; rather solid, and 
not displaying the shagreened pattern ; with the lateral teeth 
short, but not so much so asin the other species, somewhat 
* As so little is known of this genus, I append a description of a perfect and 
well marked valve at present in my collection. 
Lrpron Pracunorprum, x. s.—L. t. planata, quadrata, subinequilaterali, 
ventraliter incurva, papyracea, alba, haud punctata; liris concentricis acutis, ven- 
traliter undulatis, interstitiis striis exillimis concentricis; umbonibus parvis, sed 
a linea dorsali recta valde prominentibus ; fossa ligamenti parva; dent. lat. parvis, 
extantibus, divergentibus, in umbone sitis, ad marginem dorsalem paululum excurva- 
tis ; dent. card. altera in valva nullo, aliera ?: imp. musc. haud conspicuis. 
Hab.—West Indies. Shaped like L. squamosum, but distinguished at once by 
the prominent umbos, incurved ventral margin, sharp concentric ridges, and 
absence of the shagreen pattern.—Long. -07, lat. *1, alt. 03. 
