MAZATLAN BIVALVES 135 



interstitia TiauA (rquantibus ; in valva maj ore planatis , 

 suhohsoletis, interstitiis minimis ; ligamento solido, aream rhom- 

 hoideam implente ; dent. card, in lined curvd, parvis ; margine 

 valvce majoris effosso, valvam alteram recipiendo ; costihus prop- 

 ter tenuitatem inttis monstrantihus. 



The above description is written from three heantiful ex- 

 amples in the Museum of Hugh Cuming, Esq. Fragments 

 only of young shells were found in the L'pool collection, which 

 however probably belong to the same species. It is known 

 from A. incongrua and its congeners by its light structure, 

 smooth epidermis, and especially by the ribs which are very 

 narrow on one valve with wide interstices, on the other broad 

 and flat, scarcely divided. There is a corresponding difference 

 in the donations of the valves. Long. 1'55, lat. 1"73, alt. 1'32. 

 ^ai.— Mazatlan, 3Ius. Cuming.— Do ; fragments on Spondylus 



calcifer ; L'pool Col. 



Tablet 631 contains the fragments. 



181. AeCA TUBEBCrLOSA, Sow. 



Proc. Zool. Soc. 1833, p. 19.— Mull. Syn. Test. Ttv. p. 179.— 

 Phil. Ahhild. I. pi. 1, f. %—Rve. Conch. Ic. pi. 3, f 18.— 

 Sunl. Bescr. Cat. p. IGl, pi. 18, f. 53.— C. B. Ad. Pan. 

 Shells, p. 263, no. 425. 



Comp. Area similis, C. B. Ad. Pan. Shells, p. 262, no. 422. 



Shape varying from subquadrate, sub?equilateral, to very 

 transverse, with the jjosterior part much produced ; sometimes 

 flattened, sometimes extremely swollen. Eibs very numerous 

 (about 36), close, slightly and ii-regularly tuberculous, often 

 shewing eoncentrie ridges of gi'owth. Epidermis dark brown, 

 coarse, deciduous near the \imbos, with short scaly hairs in 

 the intercostal spaces, and sometimes finer hairs on the pos- 

 terior part. Inside white : teeth numerous, rather broad. 

 Ligament coarse, solid, entirely filling up the rather narrow 

 area between the beaks. Hinge line sometimes rounded off. 

 The largest specimen measures /o??^. 2'78, lat.3'G7, alt. 25. 

 A squarish „ „ „ 2', „ 2-35, „ I'S. 



A swollen „ „ „ 2-4.5, „ 3', „ 2-35. 



JIab. — Eeal Llejos, at roots of INIangrove trees, low water, 

 Cuming. — Panama, in impalpable mud, under a Mangrove 

 thicket, near high watermark, not uncommon, C. B. Adams. 

 — Mazatlan ; very common ; L'pool Sf Havre Coll. 



