MAZATLAN BIVALVES 109 
George’s Port, N. Holland, (Peron). From its station in 
erevices at extreme high water mark, it has probably often 
escaped detection. It may hereafter be found to be one of the 
very few ubiquitous species. The Mazatlan specimens were of 
normal shape, °05 across. 
Hab.—Britain, Mediterranean, &c.: v. supra.—? Mazatlan ; 
extremely rare, from Chama and Spondylus; L’pool Col. 
Tablet 495 contains the pair (broken in opening) and 2 
opposite valves, probably belonging to each other. 
155. LAaSEA TRIGONALIS, 2. Ss. 
Lt. plus minusve trigonalt, complanaté, concentrice striata, 
umbonibus acutis ; cardine dentibus minimis ; card. 1-2 conicis, 
rotundatis ; lat. longis, gracilibus, vie monstrantibus ; fossd 
ligamenti magna, marginem attingente ; impress. muse. adduct. 
magns, subrotundaiis. 
Two specimens of this curious shell were found tightly 
wedged in the hole of a borer in a Spondylus valve. They are 
so different that they would be considered specifically distinet 
but for their position and general habit. One is very trigonal, 
Nucula-shaped, with a very projecting little conical tooth in 
one valve fitting between two very small ones in the other. 
The smaller specimen is of much more regular shape, with the 
teeth scarcely discernible. Both specimens are flat, concen- 
trically striated, with a rough epidermis, and are rather pearly 
within. A minute pair and fragments were also found, the 
former measuring ‘03 across. 
The trigonal specimen measures long. °28, lat. °3, alt. 17. 
The smallest one Ms BS aa a 7. aa Hi! LL 
Hab.—Mazatlan ; nestlmg in Spondylus, extremely rare ; 
E’pool Col. 
Tablet 496 contains the two large pairs and one small valve. 
156. P LasEa OBLONGA, x. 3s. 
4. t. obovali, transversd, inequilaterali, tumidiore, antice 
producia ; albé, epidermide cinered, horridiore, subpilosd in- 
dutd ; wnbonibus prominentibus ; marginibus undique excurvis ; 
dent. card. uno, minuto, conico, lat. gracillimis; fossé liga- 
mentt parvi, appressd. 
"Dec. 1855. t 
