190 PAPKRS KELATJNG TO NATURAL HISTORY. 



but Ibey made the veuti-al plate of one answer to the dorsal valve of the other, 

 and the anterior cephalic orifice of the pteropodous shell correspond to the po3- 

 terior byssal foramen of the bivalve ! " And, if the views I advance prove cor- 

 rect, they were precisely right. In all my previous attempts to homologize the 

 different classes, I had always met a\ ith an obstacle in the apparently aberrant 

 characters of the Brachiopods : never for a moment doubting the truth of the 

 accepted views, that indicated the regions to be called dorsal and ventral, aa 

 such, I labored in vain. When I undertook to interpret the relation of these 

 classes on the principle of cephalization, I found that these accepted views 

 must be doubted, and it was witli amazement that I beheld such unlocked for 

 results : that the so-called dorsal region is really the ventral region." 



To us the viev? entertained by the author, of the dorsal and ventral 

 surfaces of Brachiopoda, or Palliobranchiata, does not appear to be 

 the greatest difficulty. We suspect that the Molluscoidea of Milne- 

 Edwards — the Anthoid MoUusks of Dana — though by no means ju- 

 diciously separated as a sub-kingdom, really form together one class. 

 The Monomyarian Lamellibranchiates, on the other hand, need by 

 no means be separated from the rest of that class ; but we are well 

 persuaded that no natural and useful view of Molluscan animals can 

 ^ver be given without treating Pteropoda as a distinct class. The 

 special organs which mark them out as the expression in their sub- 

 kingdom of motory power are highly characteristic. The compara- 

 tively small extent of the class, which really indicates that motory 

 power is opposed to the Molluscan plan of structure, is certainly no 

 argument for uniting it with Gasteropoda ; and if tlie detection of 

 certain homologies of parts were so we might soon compress the whole 

 sub-kingdom into a sinsle class. The stiucture and arrangement of 

 the suckers, in some speries, would of itself alone go far with us to 

 confirm Cuvier's view of tin position of the class, as next to Cephal- 

 opoda. 



We thus arrive at five classes, rcjiresenting five tendencies of struc- 

 ture, which we believe to be everywhtrre cbsprvnble throughout th« 

 animal kingdom ; and our great difference from Mr. Morse, in our 

 conception of the true classes in this sub-kingdom, interferes with 

 our power of immediately estimating and applying some considefa- 

 tions offered by him, which deserve attention, and possess interest. 

 His speculations respecting polarity we could not make intelligible in 

 few words without the convenience of figures. His concluding re- 

 marks are rendered obscure and repulsive by Prof. Dana's peculiar 

 and highly objectionable terminology. Takiug it as a whole, this 

 short essay is of considerable importance, and proves its a\(thor to be 



