ON PHORONIS OVALIS, STRETHILL WRIGHT. 
125 
tlie original figures, has a simple structure, its ends not being 
in-rolled. In this respect it agrees with P. ovalis; but 
Van Beneden’s figures represent animals with about forty 
tentacles, a number which is considerably in excess of that 
given by Stretliill Wright for his species, and of that found 
by myself in the Northumberland material. De Selys- 
Longchamps (1903, p. 25) has found a form at Heligoland, 
which he refers to Van Beneden’s species; and in support of 
this conclusion he emphasises the occurrence, in the Heligo- 
land specimens, of very numerous epidermic structures (see 
his Plate ii, figs. 22-26), which he identifies with Van 
Beneden’s. “ hairs.” This resemblance is certainly a striking 
one, especially as the author points out that he has not found 
these structures in any other species. The number of 
tentacles found by de Selys-Longchamps was, however, 
greater than that given by Van Beneden, being commonly 
fifty to sixty, but sometimes as much as eighty. The length 
of the tube of the Heligoland species is said to be 10-20 mm. 
It may be remarked that P. h i ppocrepia, P. gracilis, 
and P. ovalis are all found in burrows in the shells of 
Molluscs, or in other calcareous substances. They appear to 
differ from one another in size and in the number of their 
tentacles; P. hippocrepia having the largest dimensions 
and the greatest number of tentacles, P. ovalis occupying 
the other end of the series in both respects, and P. 
gracilis taking an intermediate position. 
P. millleri, also described by de Selys-Longchamps 
(1903, p. 6) from Heligoland, does not form colonies. It 
reaches a length of 40-80 mm. and has fifty to sixty 
tentacles, of which those on the oral side of the lophophore 
are specially short. 
Structure of P. ovalis. 
The general structure of the members of this genus is so 
well known 1 that it will not be necessary to describe that of 
1 See especially the elaborate monograph of de Selys-Longchamps 
(1907), who gives full references to the literature of the subject. 
