20 University of California Publications in Zoology. [Vol. 4 



posed. Right gonad close to the endostyle and extending parallel 

 with it. 



A single specimen from station 4420, east point of San Nic- 

 olas Island, S. 77°, W. 5.7 miles, April 12, 1904, 33 fathoms, 

 bottom fine gray sand. 



Judging from certain other species of simple ascidians that 

 present considerable variability in the distance apart of the ori- 

 fices, we may suppose that acquaintance with more specimens of 

 31. transvcrsus will find the unusual form of this particular indi- 

 vidual not to be M'holly constant for the species. We may be 

 quite sure, however, that an exceptionally wide separation of the 

 siphons is characteristic of the species. 



As to general form M. transversus is approached in the re- 

 moteness of its siphons by M. arenaceous Sluiter (Sluiter 1904), 

 but this latter species lacks considerable of being so nearly a 

 cylinder with orifices at opposite ends, as is the particular speci- 

 men of 31. transversus under observation. Furthermore M. are- 

 naceous has a thin leathery test bearing numerous processes, and 

 is covered more or less completely with sand. 31. transversus is 

 peculiarly smooth surfaced and free from sand. When note is 

 taken of the fact that the animal comes from a sandy bottom, 

 this trait as distinguishing it from 31. arenaceous becomes of 

 special weight. Another equally important distinction between 

 the two species is found in the hypophysis mouth. This in M. 

 arenaceous is broken up into a number of wholly distinct parts. 



On the whole 31. transversus appears to be a specially well 

 defined species. It should be said, however, that in a few par- 

 ticulars of internal structure a more careful examination of more 

 specimens may somewhat modify the diagnosis. For example, I 

 am considerably in doubt about the number of tentacles. It is 

 not impossible that a minute branchial fold may be present on 

 each side next to the endostyle. The dorsal lamina should also 

 receive more study. Again attention ought to be called to the 

 fact that the stomach is not in reality so positively folded as 

 fig. 23 gives the impression that it is. The folds are very small 

 and may be easily overlooked. 



