328 
ON XYLOPHAGA PRZAESTANS, n.syp., FROM THE ENGLISH COAST. 
By Enear A. Suiru, F.Z.S., ete. 
Read 3rd April, 1903. 
Tue shells upon which the following observations are based were 
kindly placed in my hands by Mr. J. R. Le Brockton Tomlin: he 
obtained them from a fisherman by whom they had been extracted 
‘‘from an old mast at Blyth”? on the coast of Northumberland. 
The specimens were sent to me as a donation to the Museum 
collection. They are of very great interest, being much larger than 
any other specimens of the genus hitherto obtained, and differimg to 
such an extent from the type of the genus, the well-known Xylophaga 
dorsalis of Turton, that I feel justified in considering them as belonging 
to-a distinct species, which may be thus described :— 
1. XYLOPHAGA PRHSTANS, 0.sp. 
Testa X. dorsal’ similis sed major, area antica filiis fortioribus et 
magis distantibus instructa, linea arcuata impressa ab umbone ad 
angulum anticum sculpta, laminis duobus dorsalibus (protoplaxibus) 
formee dissimilis et diverse positis; cicatrix postica intra valvas 
rugose striata. Diam. 18mm., longit. umbone ad marginem 
ventralem 17°5 mm. 
After a preliminary examination it seemed doubtful whether it 
might not be equally advisable to regard this interesting form as 
a variation of X. dorsalis rather than as a distinct species. It appeared 
to be one of those perplexing cases, with which the zoologist is 
frequently confronted, in which the evidence of so-called specific 
distinctness is not at all conclusive, and yet is sufficient, if constant, 
to warrant a separation. 
In the first place the size greatly exceeds that of any recorded 
specimen of X. dorsalis; secondly, the sculpture of the anterior 
triangular area is different, the parallel raised lines being conspicuously 
further apart and crossed by a depression or impressed line, which curves 
from the umbones to the anterior angle, marking off a lunule-like space ; 
thirdly, the raised lines on the narrow surface between the anterior 
triangular area and the anterior subobsolete keel spread out more con- 
spicuously behind; and finally, the dorsal accessory plates (protoplaxes 
of Fischer) are not of the same form, and fit on to the valves in a different 
manner. ‘They vary somewhat in different specimens, but in no case 
do they resemble those of typical examples of the species. In most 
instances the upper surface of each plate is acutely triangular, and 
stands almost erect from the portion of the plate which is doubled under 
and rests upon the surface of the valve. This part of the plate is 
erooved on the under side, the groove ending in a notch on the outer 
or lateral margin. There is another difference which, although not 
