ORTMANN : TERTIARY INVERTEBRATES. 253 
of a longitudinal furrow; spur broad, with the end truncated, situated 
very near or quite close to the basi-scutal angle. 
Remarks : There is no doubt that our fossil species belongs in the 
neighborhood of B. trigonus and spongicola Darwin (ibid., p. 225, pi. 4, f. 
1), but it is hard to say with which one of these it is to be classed. I 
possess 4 sets, of which I have procured scuta and terga, the latter corre- 
sponding closely to the figures given by Darwin (especially fig. y a on pi. 
3). The scuta also agrees in general form, especially two taken from a 
colony of young ones (on Terebratella giganted)'. in these the rows of pits 
are quite distinct and numerous (about 6). In other scuta (3 taken from 
colonies upon Ostrea ingens ), these pits are hardly or not at all visible, 
and the adductor ridge is more prominent, so that I am not quite satisfied 
that they really belong to this species. A character that would speak 
against the union of our specimens with B. trigonus is the complete lack 
of ribs on the parietes : but, according to Darwin, such a variety is known 
in B. trigonus . 
B. spongicola is characterized by the lack of these ribs, and, further, 
the existence of numerous (6) rows of pits on the scutum, giving rather 
a radially striated appearance to it, would tend to approximate our spec- 
imens to B. spongicola. In this species, however, the apex of the tergum 
is sharply pointed or beaked, which is not the case in B. trigonus , nor in 
any of our terga. 
Thus, it seems that our fossil form is in some degree intermediate 
between B. trigonus and spongicola, which is not astonishing at all, since 
Darwin points out the close resemblance of both. 
It is not certain that all the specimens recorded here really belong to 
this species ; the outer form of the shell is indistinguishable from that of 
the following species. The single individuals, however, are distinctly 
larger, with the exception of those of a colony on Terebratella gigantea , 
which are of about the same size as those of the colony of B. Icevis 
described below. Height of largest individual, 16 mm, diameter at base, 
27 mm. 
Record of specimens: Cape Fairweather, ca. 12 more or less isolated 
specimens ; three colonies, one on Terebratella gigantea , two on Ostrea 
ingens. 6 scuta, 3 terga. 
Distribution: Recent, almost cosmopolitan; at any rate, circumtrop- 
ical (Weltn.). It has been found on both sides of South America: 
