1853.] RIBEIRO AND SHARPE — BUSSACO. 155 



The specimens figured by M, Rouault are much distorted, and 

 only show the exterior, for which reason the species is re-figured 

 here. It is interesting as a connecting link with the Lower Silurian 

 strata of Brittany, and should teach us caution in assigning an age 

 to unknown strata from the general form of a shell without strict 

 attention to specific differences ; as, had this species been found alone, 

 most palaeontologists would have referred it to the Carboniferous 

 period. 



Plate VIII. fig. 4 a. Dorsal valve, exterior. 



Fig. 4 b. Dorsal valve, interior. 



Fig. 4 c. Ventral valve, exterior. 



Fig. 4 d. Ventral valve, interior. 



PoRAMBONiTES, Pander in^art. 



A slightly-inequivalved brachiopod with both valves convex, and 

 with a rounded or ovate outline ; hinge-line very short, with a very 

 small area and small triangular opening below the umbo of each valve : 

 two strong dental plates on each valve with their bases parallel and 

 approximate : surface of the shell punctated. 



In the second volume of the ' Geologic de la Russie d' Europe,' 

 p. 128, M. de Verneuil has brought together under the section of 

 S]ih'ifers anormaux, equirostres, a group of shells which had first been 

 published under the generic name oi Porambonites by M. Pander, 

 along with some others which belong to different genera. The cha- 

 racters which separate these species from the normal form of Spirifer 

 are their oval form, with very short hinge-lines ; an area and opening, 

 with a pair of strong dental plates to the hinge of each valve, and 

 the punctated structure of the shell. They are allied to Spirifer 

 biforatus in the double area and opening and in their punctated 

 structure ; but they differ from that species in their oval form and in 

 having similar dental plates on both valves. In form and internal 

 structure these species approach nearer to Pentamerus than to Spi- 

 rifer, but the dental plates differ materially from those oi Pentamerus, 

 and the punctated structure forms another distinction which must 

 never be overlc'ked in the classification of the Brachiopoda. I 

 propose, therefore, to place these shells in a separate genus, restoring 

 to them M. Pander's original name of Porambonites, as has already 

 been done by Prof. M'Coy. The following species published by 

 M. de Verneuil belong to this genus : Spirifer reticulatiis, S. poram- 

 bonites, S. cequirostris : three others, S. Tcheffhini, S. rectus, and S. 

 Panderi, require farther examination of their internal structure to 

 decide whether they belong to this genus, or are to be classed with 

 S. biforatus in some other genus. Professor M'Coy qiiotes one 

 species of this group from the Upper Tweed ; and it is probable that 

 Atrypa crassa, Sil. Syst., and Terebratula Capewellii, Davidson, will 

 have to be placed in it. 



Two new species of the same genus occur in the collection sent by 

 M. Ribeiro from Bussaco, which are distinguished by their large 

 size compared with those previously known, and by having no sinus 

 nor mesial fold. 



VOL. IX. — PART I. M 



