MAZATLAN BIVALVES 135 



interstitia hand cequantilus ; in valvd majoreplanatis, 

 subobsoletis, interstitiis minimis ; ligamento solido, aream rhom- 

 boideam implente ; dent. card, in lined curvd, parvis ; marginc 

 valvtz majoris ejffosso, valvam alter am reeipiendo ; co stilus prop - 

 ter tenuitatem intus monstrantibus. 



The above description is written from three beautiful 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 crenations of the valves. Long. 1*55, lat. 1*73, alt. I' 32. 

 Hob. Mazatlan, Mus. Cuming. Do ; fragments on Spondylus 



calcifer ; L'pool Col. 



Tablet 631 contains the fragments. 



\- 184. AECA TUBERCULOSA, Sow. 



Proc. Zool. Sac. 1833, p. 19Miill. Syn. Test. Viv. p. 179. 

 Phil. Abbild. I. pi. 1, f. 2.Rve. Conch. Ic. pl.-3, f. 18. 

 Hani. Descr. Cat. p. 161, 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, subsequilateral, to very 

 transverse, with the posterior part much produced ; sometimes 

 flattened, sometimes extremely swollen. Bibs very numerous 

 (about 36), close, slightly and irregularly tuberculous, often 

 shewing concentrie ridges of growth. Epidermis dark brown, 

 coarse, deciduous near the umbos, 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 long. 2 '78, lat. 3*67, alt. 2 '5. 

 A squarish 2', 2*35, 1*5. 



A swollen 2'45, ,,3', 2'35. 



Hab Real Llejos, at roots of Mangrove trees, low water, 

 Cuming. Panama, in impalpable mud, under a Mangrove 

 thicket, near high water mark, not uncommon, C. B. Adams. 

 Mazatlan ; very common j L'pool fy Havre Coll. 



