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TERTIARY FAUNA OF FLORIDA ^ 



The exterior sculpture of the Tellinas is emphatically concentric. Though 

 fine radial sculpture often exists, it does not, except in the section Pseud- 

 arcopagia, rival the concentric sculpture in strength. There is no known 

 species with only radial sculpture. Oblique or angular sculpture is rare. The 

 posterior end of the shell is usually flexed to the right and exhibits one or 

 more folds of greater or less prominence. Occasional marked inequality of 

 the valves is observable, and the culmination of the surface sculpture as it 

 passes over the ridges which radiate from the beaks towards the end of the 

 valves sometimes results in elegant lamelliform prominences. 



The characteristics of the soft parts have been already mentioned (p. 553), 

 the foot is sometimes (Psammacoma) modified to serve as a stilt or anchor, 

 much as in Yoldia, and the siphonal tubes are long and naked. The supposi- 

 tion of Fischer, that in Macoma the branchial siphon is much shorter than 

 the anal one, is incorrect. Deshayes has indeed figured a species with this 

 character (which was perhaps due to mutilation), but the common typical 

 Macomas do not show any such feature ; in them, as in most bivalves, the 

 anal siphon is shorter. If we symbolize the left valve by l, the right by r, the 

 laterals by 1, the simple cardinals by i, the bifid cardinals by yi, the resilium 

 by c, and indicate distance from or adjacency to the cardinals by the signs — 

 and -|- respectively, the normal formula for the hinge of a fully developed 

 Tellina will be l 1 — 10^0—1 ^j^^ ciphers standing for the gaps into which the 



R 1 — ojoi — 1 ^ " o i. 



teeth enter when the valves are closed. In the subgenus Angidus, which has 

 a single adjacent lateral in the right valve, possibly of different origin from 

 the distant laterals of typical Tellina, the formula will be ^ ^°^ , ^ , the right 

 hand end of the formula in all cases corresponding to the anterior end of 

 the hinge. I insert the symbol for the resilium only when it is subinternal. 

 The following subdivisions are recognizable in the genus Tellina: 



A. With tivo lateral lamina; in each valve, those in the left valve always less 



strong. 



Subgenus Tellina (Lam.) s. s. Type T. virgata Linne. 



Valves sculptured externally, the concentric sculpture stronger; somewhat 

 compressed, ovate trigonal, subequivalve, with a more or less distinct ridge 

 from the beaks towards the lower posterior angle ; subequilateral, porcellanous, 

 often elegantly colored, the periostracum hardly visible ; the umbonal radii 

 internally inconspicuous or absent, the shell margin entire, the siphonal sinus 

 more or less coalescent below with the pallial line. 



