THE SESSILE BARNACLES. 



243 



ACASTA JAPONICA Pilsbry. 



1911. Acasta spongites japonica Pllsbry, BulL Bnr. of Fisheries, vol. 29 

 (Document No. 739), p. 80, pi. 16, figs. 1-9. 



T>/pe.— Cat No. 38681, U.S.N.M., from Albatross station 4936, off 

 Kagoshima Gulf, Japan, in 103 fathoms, embedded in a sponge. 



In the absence of specimens of A. spongites for direct comparison, 

 I described this as a subspecies of that European form. Having now 

 studied a long series of the latter, I have reconsidered the matter and 

 believe that the Japanese form is specifically distinct. It is larger 

 than A. spongites; the shape of the tergum is quite different and it 



Fig. 



r7. — Acasta spongites, 



EXMOUTH, TERGUM. 



Fig. 78.- 



-ACASTA JAPONICA, TERGUM 

 OF TYPE. 



has an external depression or furrow to the spur. In A. spongites 

 there is no furrow, but the flat spur-f asciol?* is bounded by lines. 

 As there seems to be no figure of the exterior of the tergum of A. 

 spongites I am illustrating it here for comparison with that of A. 

 japonica, both figures being drawn to the same scale. The sculpture 

 of the scutum is stronger in\4. spongites, the longitudinal grooves 

 more emphatic. In A. japonica the longitudinal sculpture is of nar- 

 row raised threads. Finally, the proportions of the valves are dif- 

 ferent. In A. spongites the length of the tergum is but slightly more 

 than three-fourths that of the scutum. In A. japo7iica it is seven- 

 eighths. The breadth of the tergum is less than that of the scutum 

 in .4. spongites, but in the Japanese species both valves have the same 

 maximum breadth (fig. 78). 



