48 CARBONIFEROUS LAMELLIBRANCHIATA. 



decide to include in Streblopteria, " smooth little Carboniferous and Permian 

 species, which seem to have generally, if not always, a deep sharply-defined byssal 

 sinus in the anterior margin of the right valve." 



These authors propose to refer to this genus such forms as Pecten dissimilis 

 and P. consimilis, M'Coy, and refer an American species, previously described by 

 themselves as P. tenuilineatus, to the genus. 



I cannot think it wise to extend the genus Streblopteria to receive shells with 

 well-marked posterior ears, especially when Meek and Worthen state in tbeir 

 description, "posterior wing broad, undefined, nearly rectangular, extended nearly 

 as far as the posterior margin of the shell," and I cannot admit that their shell 

 belongs to this genus. It is difficult to understand on what grounds they would 

 refer P. dissimilis, with its well-marked ears and its strongly ribbed character, to 

 Streblopteria. Pecten consimilis, M'Coy, a synonym of Pecten anisotus, Phillips, 

 has a small, not extended, well-defined posterior ear, and therefore not belonging 

 to this genus, from which it also differs in being ovate and having no expanded 

 anterior margin. 



De Koninck accepted M'Coy's genus and described eighteen species, of which 

 I think 8. elongata, M'Coy, sp., 8. prselineata, 8. picta, 8. pullus, 8. eUipsoidea, 

 S. propiiiqiia, having well-marked posterior ears, do not belong to the genus. I 

 am not prepared, however, to accept all the other species, as I suspect some of 

 them represent different stages of growth of the same shell. I find that the length 

 of the hinge-line and the development of the posterior wing vary greatly with each 

 stage of growth. 



Streblopteria seems to form a passage between Posidoniella and Posidonomya 

 and a more strictly Pectiniform type. The two former genera have no anterior 

 ear, or a very rudimentary anterior ear respectively, but both have a rectangular 

 expanded posterior wing. Eumicrotis, too, would seem to come even between 

 Posidoniella and Streblopteria, because in that genus the right valve has a well- 

 marked anterior ear, separated by a deep and long slit for the byssus from the 

 rest of the valve. There is no evidence that Posidonomi/a was byssiferous, but 

 Posidoniella often occurs in numbers attached to fossil vegetable remains. 



Streblopteria l.evkjata, M'Coy, 1855. Plate XI, figs. 1 — 7. 



Mbleagbina l.evigata, M'Coy, 1844. Syiiops. Carb. Foss. Ireland, p. 80, pi. xii, 



fig. 5. 

 Aviculopecten l^evigatub, Morris, 1854. Cat. Brit. Foss., 2ml edit., p. 165. 

 Streblopteria laevigata, M'Coy, 1855. Brit. Pal. Foss., p. 482. 



— de Koninck, 1885. Aun. Mus. Eoy. d'Hist. Nat. Belg., 



torn, xi, p. 203, pi. xxxii, figs. 2, 3 ; pi. xl, figs. 14, 15. 



