38 



Bute ill August, 1888. It measures as mounted about 0-8 mm., 

 and possessed 13-14 pairs of tentacles. j\Ir. James Dick, M.A., 

 Glasgow, through the kmd offices of Dr. Gemmill, was also good 

 enough to send me a number of carefully made mounts of Actino- 

 trocha from the Ctyde. One was as small as 0-57 mm., and had 

 only six pairs of tentacles, and the appearance of de Selys Long- 

 champs Fig. 11, Plate II., of A. hatsckeki ; some had twelve pahs 

 of tentacles, and two had evidently about seventeen pairs of 

 tentacles. It is difficult to identify species in the case of 

 preserved specimens, but I came to the conclusion that the 

 Clyde larvae also belonged to this species, even the small one 

 mentioned, for similar specimens have been got at St. Andrews. 

 Besides the locaHties already given, tha larva is common in the 

 Mediterranean, at aU events, at Naples and in the Adriatic. De 

 Selys Longchamps says it is found at Plymouth, but according to 

 Allen (in a letter) the Actinotrocha they get is the larva of P. 

 hippocrepia. 



It is evident then that Pkoronis ovalis is more widely spread 

 than the records indicate, and it is probable therefore that it is 

 Hable to considerable modification as we have seen the larva is. 

 The tentacles of the larva during its period of growth are added 

 to in pairs, and metamorphosis may take place before the maximum 

 number is reached. As wiU be apparent presently the adult also 

 adds to its number of tentacles in the same manner. The tenta- 

 cular crown moreover is hable to be thrown off and renewed. We 

 cannot therefore insist too strongly on the number of tentacles 

 as a specific feature. The shape of the lophophore is probably 

 more constant, but in the same species it is hable to be more folded 

 inwards in some of the examples than in others. The size, as 

 Harmer has indicated, is very variable. The characters are thus 

 very vague, and in detailing them hberal use of numbers and 

 descriptions must be admitted. Probably the character which 

 might with most reason be appealed to is the number of longi- 

 tudinal bands of muscles in the upper half of the metasome, 

 but even this is variable. Pkoronis ovalis has only been found 

 hitherto in shells, but so rarely that it need not surprise us to 

 find that it may have to be content to form its tube in sand or 

 in stones, and, if so, it may be found to vary according to the con- 

 ditions. We have to remember too the long denatation to which 



