NO. 1989. ASCIDIANS FROM NORTHEASTERN PACIFIC— RITTER. 437 



vessels in the folds of the brancliial sac. The largest number in any 

 group — the "areiiata group" — is given as 4 to 6. On this basis 

 M. oregonia would not fall into any of the recognized groups, for the 

 number here is always and very definitely greater. The scheme of 

 vessels in a typical specimen is: 



-c, , , T 17-0-9-1-10-1-10-1-11-0-8 L. 



^""^^'^y^r-i-io-i-ii-i-ii-i-ii-o-ion. 



While in some genera of ascidians the variabihty in the number of 

 vessels is so great, and the difficulty of counting so considerable that 

 the excess m the numbers here given over the numbers in J/, impura 

 might not be regarded as significant unless based on the averages of 

 many individuals, the numbers in the species of Molgula with which 

 we are now deahng are so constant and so definitely determinable, 

 that there can bo no question about the specific significance of the 

 differences, ijarticuiarly since these are correlated mth other small, 

 but seemingly constant difi^erences. 



Albatross 3088 (type-locality), lat. 44° 28' N.; long. 124° 25' 30" 

 W., off Oregon, 46 fathoms, c. p., September 3, 1889, 16 specimens. 



Albatross 3213, lat. 54° 10' N.; long. 162° 57' 30" W., South Alaska 

 Peninsula, 41 fathoms, bk. s.. May 21, 1890, a single specimen. 



Type.—Csit. No. 5682, U.S.N.M. 



MOLGULA RETORTIFORMIS Verrill. 



Molgula retortiformis Verrill, 1871, p. 56, fig. 3. 



Molgula groenlandica Traustedt, 1880, p. 425. — Wagner, 1885, pp. 124-150, pi. 



15, figs. 1-9; pi. 16, figs. 1-8, 13, and 15; pi. 17, figs. 1-17; pi. 18, figs. 11 and 



13; pi. 20, figs. 2, 3, and 16-18. 

 Molgula siphonalis Hartmeyer, 1899, p. 462, fig. B; pi. 22, fig. 2; pi. 23, figs. 2 



and 13. 

 Molgula grapMca Ritter, 1901, p. 230, pi. 28, figs. 6-9. 

 Molgula retortiformis Hartmeyer, 1903, p. 145. 

 Caesira retortiformis Hartmeyer, 1909a, p. 1324. — Van Name, 1912, p. 510, text 



figs. 18 and 19; pi. 52, figs. 50-52; pi. 69, figs, 139, 140. 



There being available for comparison several specimens of J/oZ- 

 gula retortiformis from Marthas Vineyard identified by Prof. A. E. 

 Verrill, I do not now hesitate to confirm Hartmeyer's conjecture that 

 Jf. graphica Hitter is only a synonym for 21. retortiformis. The spe- 

 cies is obviously a rather common inhabitant of the shallow waters 

 of the northeastern Pacific and Bering Sea. 



I have examined the single specimen on which M. grapJiica was 

 founded, giving special attention to the network of jet black blood 

 vessels in the test on which I relied so largely for the vaUdity of the 

 species. The vessels themselves differ in no recognizable way either 

 in structure, abundance, or distribution from those in the test of the 

 Marthas Vineyard specimens or specimens from Bering Sea. The 



