The Austral Rhynchonellacea. 



183 



san; Stansbury, Yorke's Peninsula; River Bremer at Salem, near Cal- 

 lington. Victoria. — Aire Coast; Fishing Point, Cape Otway; Lower 

 Moorabool; Maude; Curlewis; Flinders; Waurn Ponds; Keilor. 



3. — Tegulorhynchia thomsoni, sp. nov. 

 (PI. I., figs. 5, 6; pi. II., figs. 18, 21; pi. III., fig. 28.) 



Description. — Shell subovate, tending to subglobose in shape, 

 slightly wider than long. Shell stout, as in T. coelata.. Delthyrium 

 is large and open. Deltidial plates strong, triangular and nearly 

 equilateral, reminding one of similar characters in T. nigricans. Sinus 

 not so deep as in T. coelata. Surface of valves, especially the ventral, 

 showing interrupted growth stages. Twenty-eight plicae seen on ven- 

 tral valve, six on the sinus. Beak not forwardly projecting, but 

 truncated; deltidial plates discrete. 



Dimensions. — Length, 17 mm.; width, 20.5 mm.; thickness of 

 valve, 10:25 mm. Greatest width of delthyrium, 2.5 mm. 



Otservations. — This species occurs in company with T. coelata, 

 T. Woods, at Table Cape, and it is interesting to note that the pre- 

 sence of two species was also suspected by Dr. J. Allan Thomson 

 a few years ago. In 1914, in a letter to one of us he says: "There 

 are two species at least at Table Cape. One appears to be H. squamosa, 

 and this wasj probably the one called R. coelata by McCoy. The other 

 is coarser ribbed and less squamose, and is also, I think, represented 

 in New Zealand, but I would like to see a larger series of specimens 

 before making a definite statement." 



The differences between the shells of the above species and 

 T. coelata are easily seen when a comparative series is laid out. These 

 differences are as follow: — 



T. thomsoni. 



T. coelata. 



Beak more prominent, approaching 



Beak not prominent, apex rounded 



that of T. nigricans. 



in edge view, not incurved. 



Plicae stouter and less numer- 



More numerous. 



ous. 

 Six plicae on sinus. 



Eight plicae on sinus. 



The growth-lines not conspicuous 



Tegiulation and growth-lines 



until reaching the beginning 



clearly at the beginning of the 



of the ephebic stage. 



neanic stage. 



Convexity more evenly distribu- 



Dorsal valve tends to become ex- 



ted on both valves. 



tremely convex, and the fold 





on the sinus is more pro- 





nounced. 



Lateral cardinal area evenly con- 



Compression of the lateral car- 



vex. 



dinal area pronounced. 



Foramen large and rounded. 



Foramen oval. 



Deltidial plates equilateral; dis- 



Deltidial plates vertically length- 



crete, but less so than in 



ened; discrete. 



T. coelata. 





