392 DR. W. T. CALMAN ON 



posterior margin, beginning on the dorsal side, just behind the- 

 liinge-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 maiinii, mentioned below, the auricle and nearly the whole 

 of the postero-median area have been removed, while the antero- 

 median {vertically striated) area occupies the greater part of the 

 sui'face of the valve. It may be suggested as a possibility that 

 the absence of extensive erosion in most specimens of T. navalis: 

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

 annual species, the individuals rarely surviving the winter, while 

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

 pei'haps surviving for several years in the warmer waters which 

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

 important to ascertain the duration of life and the rate of gi-owth 

 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 



sarrounds the bases of siphons and palettes" as the chief 

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

 name Calohates of Gould, and later (Mem. Austral. Mus, Sydney, 

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

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

 figures of Forbes and Hanley and other writers," 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 appears 

 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, entii-ely similar to that 

 found in Teredo mannii and various other species which Hedley 

 refers to JSfausitora or Calohates. 



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



Teredo navalis Linnseus, Syst. JSTat. 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 j^^dicellata Quati'efages, Gwyn Jeffreys, Brit. Conch, 

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



* Gvvj'n Jeffreys' description of the " vav. divaricata " of T. norvagica, tlie 

 " var. occhisa " of T. navalis, and the analogovis varieties of other species, as well as 

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

 are based on unusnally 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. 



