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. 

 i), 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. 7" on pi. 

 3). The scuta also agrees in general form, especially two taken from a 

 colony of young ones (on Terebratella gigantea]: 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. trigomis is the complete lack 

 of ribs on the parietes : but, according to Darwin, such a variety is known 

 in B. trigomis. 



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 gigantca, 

 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: 



