I 



392 DR. W. T. CALMAN ON 



posterior margin, beginning- on the dorsal side, jnst behind tlie 

 hinge-knob, and extending downwards. The rapidity and extent 

 of this erosion appears to difter in different species. Incon- 

 spicuous, as a rule, in T. navalis*, it becomes very marked in 

 certain tropical species. For example, in many specimens of 

 Teredo mannii, mentioned below, the auricle and nearly the whole 

 of the postero-median area have been removed, while the antei'o- 

 media.n (vertically striated) area occupies the gi eater part of the 

 surface of the valve. It may be suggested as a possibility thajt 

 the absence of extensive erosion in most specimeiis of T. navalis 

 is due to the fact that this is a short-lived and indeed almost an 

 annual species, the individuals rfa^ely surviving the winter, while 

 the much larger T. mannii may be longer lived, the individuals 

 perhaps surviving for several years in the wai-mer waters which 

 it inhabits. From the practical point of view^ it would be very 

 important to ascertain the duration of life and tlie rate of growth 

 in the different species. 



Genus Teredo Linn. 



Hedley (Proc. Linn. Soc. N. S. Wales, xxiii. 1898, p. 92) 



regarded the presence of a " cup-shaped mantle which 



surrounds the bases of siphons and palettes" as the chief 

 distinctive character of a genus to which he applied at first the 

 name Ccdohates of Gould, and later (Mem. Austial. Mus. Sydney, 

 iii. 1899, p. 508) Nausitoria (i. e. Nausitora) of Wright. Hedley 

 states that the type of the genus Teredo, "according to the 

 figures of Forbes and Hanley and other w^riters," entirely lacks 

 this structure. The accompanying figure (text-fig. 1, A) is taken 

 from a well-preserved specimen from the estuary of the Thames, 

 for which I am indebted to Dr. W. M. Willoughby, Medical 

 Officer of Health for the Port of London. This specimen appeais 

 to be referable, without doubt, to the typical T. navalis Linn. 

 It will be seen that the base of pallets and siphons is surrounded 

 by a fleshy collar or fold of the mantle, entirely similar to that 

 found in Teredo mannii and various other species which Hedley 

 refers to Nausitora or Calobates. 



Teredo navalis Linn. (Text-fig. 1.) 



Teredo navalis Linn^us, Syst. JN^a.t. ed. x. 1758, p. 651 ; Forbes 

 and Hanley, Hist. Brit. Moll. i. 1848, p. 74, pi. i. figs. 7, 8, 

 pi. xviii. figs. 3, 4 ; Gatliff and Gabriel, Proc. R. Soc. Victoria, 

 xxviii. (n. s.) 1915, p. 117. 



? Teredo pedicellata Quatrefages, Gwyn Jeffreys, Brit. Conch, 

 iii. 1865, p. 174, and v. 1869, pi. liv. fig. 3. 



* Gwyn Jeffreys' description of tlie " var. divaricuta " of T. norvagica, tlie 

 " var. occlusa " of T. navalis, and the analogous varieties of other species, as well as 

 the specimens named hy him in the Norman collection, suggest that these varieties 

 are hased on unusually old specimens, in which the antero-median area occupies a 

 much larger portion than usual of the surface of the valves while the auricle has 

 been almost completely removed. 



