TRANSACTIONS OF WAGNER 

 IOO8 



TERTIARY FAUNA OF FLORIDA 



except in cases where erosion has set up a diseased condition, nor that the 

 resilium has become separated from the ligament to form an internal and 

 distinct bond between the valves, as in Semele or Abra. 



The valves of many species, especially compressed and thin forms, are 

 often strengthened by a deposit of shell-material in radial lines, which gen- 

 erally pass from the beaks towards the margin behind the anterior adductor 

 scars, and less frequently in front of the posterior scars. In the cases I have 

 noted of the latter kind there is a tendency to form two adjacent small rays 

 (as in T. fabula Gronovius), while the anterior radii are usually single and 

 stronger (T. compresxa Brocchi). The radii are sometimes well denned (as 

 in the species last mentioned), but quite frequently they have only one well- 

 defined margin. All stages intermediate may be observed in a large collection 

 of species. 



The posterior adductor scars in Tellina are generally rounded, the anterior 

 ones longer and narrower. The scar of the mantle attachment is usually 

 parallel to the margin of the valves. The scar of the sinus or impression of 

 the siphonal retractors is quite variable. In some species the sinus is quite 

 free, ventrally, from the pallial line ; in the majority the two are more or 

 less coalescent, and in still others the dorsal portion of the line extends from 

 one adductor scar to the other. These may have the ventral portion absolutely 

 coalescent with the pallial line throughout, as in Strigilla (sincera, Hani.), 

 or from the adductor scar the siphonal line may run downward and back- 

 ward, enclosing a small triangular space between the pallial and siphonal lines 

 and the scar of the anterior adductor. Still another state occurs in which the 

 sinus may not reach forward, even near to the adductor, but from the latter 

 to the anterior part of the bight of the sinus a line of attachment extends (as 

 in T. scobinata L.), leaving a distinct scar. This is probably connected with 

 some reinforcement of the retractor muscles of the siphons. It is not common 

 to all the species of Arcopagia, does not occur in T. crassa, for instance, 

 which is much the same shape as T. scobinata, nor is it confined to rounded 

 species, since the elongated T. Antoni Phil, exhibits it. I have called this 

 a case where the sinus is " linked" to the adductor. 



I have not found the details of the disposition of the scar of the sinus 

 very constantly correlated with the other characters of the shell, and in the 

 Macomas a notable amount of variation may occur within the species. As I 

 have elsewhere observed, its physiological importance cannot be very great 

 and caution should be used in basing systematic subdivisions on this character 

 alone. 



