274 DE. W. A. HEEDHAN ON BRITISH TUFICATA. 



is itself invisible, but is very strongly defined by the deep undulated 

 furrow, which at the top of the whorls sinks in behind the longi- 

 tudinal ribs and cuts them off from the base of the preceding 

 whorl. Mouth oval, rather small, deep, perpendicular, and very 

 little oblique ; from its lower left corner rises a strong, deep, 

 equal, slightly curved canal, whose direction is distinctly, but not 

 strongly, to the left. Outer lip : its nearly semicircular curve is 

 slightly flattened about the middle, and bags a little toward the 

 lower outer corner ; at its upper corner it advances a good deal 

 and rises a little on the body-whorl ; its sharp and contracted 

 margin, which projects from the last and massive varix, is crenu- 

 lated ; remote from the edge it is scored by 9 rather long, narrow, 

 sharp-topped teeth, the first and two last of which are stronger 

 than the rest ; the first is a little remote from the upper angle 

 of the mouth, while the last is on the very edge of the canal. 

 Inner lip spreads patulously, but not broadly, on the body- 

 whorl in a thin, defined, porcellauous layer ; it runs straight 

 down the pillar as a sharp projecting edge ; it is scored within 

 by about 9 teeth, of which the first is short and strong, the 

 second long and strong, the third and fourth long and weak, the 

 fifth, sixth, and seventh short and weak, while the eighth and 

 ninth are strong and coil round the point of the pillar. On the 

 left side of the canal are 4 or 5 tubercles. H. 1-37. B. 0-84. 

 Penultimate whorl, height 0*26. Mouth, height (exclusive of 

 canal) 049, breadth 0"3. Length of canal 0-29, breadth 0-07. 



This species has much resemblance to A 7 ", acuminata, Eve., but 

 is shorter, squatter, coarser, with more ribs, is deeper in suture ; 

 tbe canal is shorter, more recurved, and more twisted. 



Notes on British Tunicata, with Descriptions of new Species. 

 I. Ascidiidae. By "W. A. Heedman, D.Sc. Edinb. 



[Communicated by Sir Wyville Thomson, F.R.S., F.L.S.] 



[Read December 2, 1880.] 



(Plates XIV.-XIX.) 



The family Ascidiidae comprises those Simple Ascidians which 

 have a six-, seven-, or, more generally, an eight-lobed branchial 

 aperture and a six-lobed atrial aperture, the principal additional 

 characters being :—body sessile, attached ; tentacles simple, fili- 



