440 DR. WHEELTON HIND ON NAIADITES IN [Aug. 1 894, 



I have a series of specimens from the South Joggins labelled by 

 Sir J". William Dawson Anthracoptera carbonaria. They existed 

 in very large numbers in some of the shales of the South Joggins, 

 so much so that the greater part of the mass is composed of debris 

 of this shell, with entomostraca and vegetable remains. I have 

 little or nothing to add to Sir William's original specific description, 

 but would point out that his original figure is very misleading, and 

 that Naiadites carbonarius, Dawson, differs much from the figure of 

 Anthracoptera carbonaria, Salter (Quart. Journ. Geol. Soc. vol. xix. 

 1863, p. 79), and it was tbis difference which led me to suppose 

 that Dawson's original specimen was probably Anthracomya 

 (Quart. Journ. Geol. Soc. vol. xlix. 1893, p. 249). The umbones 

 were not shown to be terminal, and were described as " acute in 

 the anterior fourth of the shell," while I thought Salter's figure 

 was that of a specimen of one of his Anthracoptera'. 



I am bound to say that Salter's figure more nearly represents 

 the shells which have been sent to me as Naiadites carbonarius. In 

 shape this form approaches somewhat to that of Naiadites {Anthra- 

 coptera) modiolaris, but the umbones are more raised above the 

 hinge-line, more pointed and not curved anteriorly at tbe apex. 



There is one specimen which reveals a typical interior with 

 finely striated hinge-plate, bevelled at the exterior of its outer edge, 

 with trifid anterior muscular scars, and relatively larger posterior- 

 adductor scar. The posterior end was often sinuated above. The 

 periostracum shows the typical characteristics of the genus. There 

 exists, as with us, an elongated form, probably only a variety of 

 this shell ; but it evidently comes from a different bed, the matrix 

 being a hard, fine-grained, micaceous sandstone (PI. XX. fig. 1). It 

 would seem to have been less gregarious in its habit, if one may 

 judge from the paucity of its remains in the specimens to hand. 



It is very difficult to be absolutely sure as to the generic position 

 of the shells figured as Anthracomya elongata, as there are no 

 specimens showing the hinge-line, ligament, or muscle-scars, but 

 from the shape they probably belong to this group. There is 

 nothing to add to the original description, but I think that the sen- 

 tence describing the position of the umbones is misleading. It says, 

 " the beaks obtuse and more anterior," but it is difficult to see what 

 is the meaning of the word more. 1 It cannot refer to the shell 

 previously described, which is a Naiadites {Anthracoptera) carbo- 

 narius, and has its umbones very forward ; while, comparatively to 

 the length of the hinge-line, the umbones in N. elongatus are sub- 

 central in the specimen figured. 



There appear to have been two forms or varieties of this shell, 

 one more elongate and comparatively narrower, the other short and 

 as broad as long. 



With regard to Anthracomya arenacea, the specimen which 

 Sir J. W. Dawson has sent me is typical of Salter's genus ; it is 

 allied to the forms found on the Continent, and known as Anodonta 



1 [A clerical error for ' less.' — J. W. D., May 1894.] 



