446 TJniversity of California Publications in Zoology [you 16 



DESCRIPTION OP SPECIES 



Note. — The formula for the number and arrangement of vessels 

 on the inner surface of the branchial membrane of simple aseidians. 

 adopted by Ritter in his later papers on aseidian taxonomy, is used 

 in the descriptions. Thus : 



,-., ( 1-7-2-6-0. etc. R. 

 e a s I 2-S-1-7-2, etc. L. 

 means that counting from the endostyle (e'd's) the vessels of the right 



side (R) number 7 6, etc., on the folds and 1- 2 0, etc., between 



the folds. The other row of numbers is self-explanatory. 



Molgula verrucifera, n. sp. 



PI. 38, fig. 5; pi. 40, figs. 15-20 



Superficial characteristics. — Regular in outline except for adhering 

 foreign bodies, nearly spherical but usually somewhat depressed and 

 covered with heaw coating of sand. Siphons not far apart and rather 

 conspicuous though entirely covered with sand (pi. 38, fig. 5). Size: 

 8 by 6 by 5 mm. ; 8 by 7 by 6 mm. ; 8 by 7 by 5 ram. ; 8 by 6.5 by 

 6.5 mm.; 8 by 6 by 6 mm.; 8 by 6.5 by 9 mm.; 10 by 8 by 7.5 mm. 

 Test thin but firm, sandy covering adhering to its numerous fine 

 processes. Mantle thin ; the longitudinal muscle bands radiate from 

 the siphons and spread out on the sides of the body so as to be sep- 

 arated by considerable spaces, extending to aboiit the middle of each 

 side. Finer circular muscle bands are confined to the siphonal regions. 

 Musculature of the two siphons about the same in strength. 



Branchial systc>n. — When removed from the test, the two siphons 

 are of about equal length although atrial is usually more slender. 

 Branchial orifice 6-lobed with tentacle-like processes inserted around 

 its edge. Of these proce.s.ses six long ones are arranged symetrically 

 and alternating with them are two smaller processes (pi. 40, fig. 18). 

 Atrial orifice 4-lobed. also with tentacle-like processes inserted on its 

 edge (pi. 40, fig. 17). Branchial tentacles 16-20, usually of two sizes 

 alternating with each other and closely crowded around branchial 

 orifice. Each tentacle bipinnate, the branches ending bluntly and 

 often swollen at tips (pi. 40, fig. 19). Hypophysis opening an elon- 

 gated slit, the ends of which may curve one way or the other to give 

 rise to the variations which appear in different individuals, situated 

 on right side of anterior end of the elongated ganglion (pi. 40, fig. 20). 

 Branchial sac witli seven well-developed folds on each side (h.f. pi. 40. 

 fig. 15), those next to the dorsal lamina very short. Formula of 

 internal longitudinal vessels : 



,-., \ i-0-6-0-6-0-6-0-6-0-6-0-3-0- R. 

 •^ *^ ^5 I .s_0-.5-0-6-0-6-0-6-0-5-0-.3-0- L. 

 The vessels are confined to surface and upper halves of the curved 

 folds, usually the same number on each side, but those on convex sides 

 always stronger. Five primary transverse vessels occur, intercepting 

 two infundibula on each fold. Secondary transverse vessels present, 



