DAYTDSOX PAL^ONTOLOGICAL NOTES OX THE BRACHIOPODA. Ill 



nences (w;), termed " oral processes " by Mr. Woodward^ and these (z) 

 I have found to correspond almost exactly with the centre of the sub- 

 spiral hollows in the ventral valve (l). It is therefore highly probable 

 that at least a portion of the arm was spirally coiled, and occupied the 

 spaee existing between and all round the conical testaceous projec- 

 tions (z) described above, as occurring in the dorsal valve, and the 

 hollow {I) in the ventral one,* in the same manner as we have shown 

 to have been the case with I)avidsonia,f but with this difference, that 

 in Froducta there exists a conical elevation in the dorsal valve, and a 

 corresponding hollow in the ventral one ; while the very reverse was 

 the case in Davidsonia and Strophomena depressa or rhomhoidalis of 

 Dalman (PI. IV. fig. 13, l). From this I would surmise that the arms in 

 the Productidce were differently disposed to those in the Davidsonidce, 

 and at least some of the Strophomenidce ; that is to say, the whole or 

 a portion of the arm formed a few vertical convolutions dii^ected 

 towards the bottom of the dorsal valve in Davidsonia and Strophomena 

 depressa, while in Producta they were, on the contrary, directed towards 

 the bottom of the hollows of the ventral one. I also consider that 

 those deep conical hollows observable in the interior of the enormously 

 thickened ventral valve of Producta humerosa, Sow., as seen in relief 

 upon the internal cast (PI. IV. figs. 3, l), to have been occupied by 

 the arms. Such is the only reliable evidence that can be offered at 

 present as to the form and position of the arms ; but it is necessary 

 here to mention that in his excellent work on the Petschoraland (pub- 

 lished in 1846), Count Alex, von Keyserhng has expressed an opinion 

 that the so-termed uniform impressions or callosities (PI. III. fig. 2, 

 and PI. IV. figs. 5, 7, 12, x) observable in the dorsal valve of all the 

 Productidce, were the probable supports of the oral arms ; which view 

 was at a later period reproduced by Mr. Howse, who, moreover, 

 assimilates those impressions to the ridges supporting the arms in the 

 interior of Argiope and Thecidium. Mr. Hancock is disposed to accept 



* In a letter I had the pleasure of receiving from Count Keyserling, it is stated, 

 that, " if in the ventral valve of Producta glgantea, and some few others, we see 

 the indication of obscure spiral depressions, this may be due to the unattached 

 portion of the anus ; but that we perceive no similar hollows in the same valve of 

 the g-reater number of species ;" but it should also be remembered that we cannot 

 expect to find hollows in those forms in which the valve was too thin to admit 

 of similar depressions. 



+ The Geologist, Vol. I., PL XII. figs. 33, 34. 



