82 



Height of the largest example (tig. B), about five inches from hinge 

 to base; approximate length of ditto, two inches and seven lines; thick- 

 ness through the valves, one inch and four lines. 



Ten specimens were collected, some of which are very imperfect. 



It has been thought desiralde to give figures and a description of 

 these fossils, for although the writer has failed to find a single character 

 by Avhich they can be satisfactoril}- distinguished from the Perna 

 mytiloides as figured by Mr. Damon and the late Professor Phillips, 

 he is by no means convinced that they belong to that species. The 

 Lamarckian definition of P. mytiloides (•' P. testa ovato-oblonga, depressa, 

 basi acuta; cardine obliqua) is altogether insufticient tor the discrimi- 

 nation of closely related forms. 



The generic name Melina of Rotzius has prioi-ity over Perna, Bru- 

 guiere. 



Syncyclonema Meekiana. (N. sp.) 

 Fig. 9. 



Fifi. 9. — Syncyclonema Meekiana.— Outline of an immature but nearly perfect ex- 

 ample, with a portion of the test of another specimen magnified to show the details of 

 the sculpture The engraver has not made the tubercles which result from the 

 crossing of the ribs sufficiently distinct. 



Shell small, compressed, thin ; subovate when half gi'own, but nearly 

 orbicular when adult ; often triangular above the middle. The ears are 

 imperfect in all the specimens ; l»ut in the upper valve they ai)pear 

 to have been horizontal above and almost vertical at the sides; those 

 of the lower valve are unknown. 



The surface of the main body of the shell is marked b}' very numerous^ 

 fine and closely-arranged, i-ounded concentric ribs, which are crossed by 

 exactly similar radiating costa3. The points at which the radiating ribs 

 pass over the concentric ones are marked by small rounded elevations or 

 tubercles, which give a nodose appearance to the sculpture, but which 

 are too small to be visible to the naked eye. The wood-cut does not 

 give a very good idea of these. Sculpture of the eavs unknown, 



