Tl'TRAPLODON 1 197 



Tr;TRAPLODON piicTiNATus Spix. 



Shell subtriangular, inflated, subsolid. inequilateral, with 

 moderately full, high beaks ; anterior end narrowed and 

 rounded ; base lightly curved ; dorsal slope arched ; posterior 

 ridge elevated, rounded, ending in a point above the base; sur- 

 face with low, radiating ridges, which become rather feeble 

 below, the dorsal slope, ridged only near the beaks. Epidermis 

 fuscous or brownish ; teeth rather delicate, elegantly vertically 

 striate ; beak cavities deep ; anterior scars impressed ; nacre 

 silvery, thinner behind. 



Length 43, height 2"], diam. 22 mm. 



Type locality, Rio Sao Francisco, Brazil. 

 Tetraplodon pectinatum Spix, Test. Fluv. Bras., 1827, p. 32, 



pi. XXV, fig. 4. 

 Tetraplodon ambiguits, (part), Simpson, Syn., icxx), p. 863. 



Spix gives two figures, 3 and 4. I believe that fig. 3 is 

 T. ambiguiis. Fig. 4 shows only the interior of two valves, 

 but they agree exactly with an old broken shell in my collection. 

 It is probably a valid species. There are other forms between 

 it and ambiguiis. 



Tetraplodon juruanus von Ihering. 



"The form of the only specimen is similar to that of T. 

 pectinatns, but the anterior end is smaller and the dorsal 

 margin slopes quite sharply to the hinder end ; a double pos- 

 terior ridge separates the side of the shell from the smooth 

 posterior slope, which is not the case in pectinatns. The epi- 

 dermis is blackish, whereas it is brown in pectinatns. The scar 

 of the anterior adductors lies in front of the cardinal tooth and 

 in front of it the anterior part of the shell protrudes as far as 

 the adductor is wide, whereas this part of the shell in pcctinatus 

 is only half the width Qi the adductor. The lateral teeth are 

 short, whereas in pectinatns they are very long. In my speci- 

 men the laterals of the left valve are 13 mm. long and the 

 distance of the anterior edge of the cardinal tooth from the 

 beginning of the lateral teeth measures the same. 



