Names were first created of Serpula bicornis ventricosa, Serpula bicornis umbilico perforato, etc, in Boys & Walker 1784) but these are not binominal and the work has been rejected by ICZN Opinion (ICZN Opinion 558 in 1959, vol 20, p.279). Names next published in Adams (1798: 633) in binominal form as Serpula bicornis and Serpula perforata. Whether the authorship should anywhere include Jacobs or Walker is very dubious, particularly as Adams uses the first person to comment on his description (such as it is). He doesn't give an authorship but would be assuming he was repeating (in altered form) the multi-word names first presented in 1784, but those names (and authors names) are unavailable. Later Turton (1802 page 609 Serpula) gives the authorship as Kanmacher & Adams. This also seems correct today, and seems to dispose of the Walker authorship, usage origin unexplained.
Boys, W.; Walker, G. (1784). Testacea minuta rariora, nuperrime detecta in arena littoris Sandvicensis / A collection of the minute and rare shells, lately discovered in the sand of the sea shore near Sandwich / by William Boys ... ; considerably augmented, and all their figures accurately drawn, as magnified with the microscopy, by Geo. Walker, bookseller, at Faversham. [Booklet]. 25 pp, published by George Walker.