48 AMERICAN JOURNAL 



confined within closed vessels, furnished with a heart and some- 

 times one or two pair of accessory " pulsatile vesicles," and a 

 series of sinuses between the laminse composing the lobes of the 

 mantle ; dioecious (?) with the genitalia usually suspended in the 

 sinuses of the mantle lobes ; the genital products expelled 

 through one or two pairs of oviducts opening externally ; prin- 

 cipal nervous ganglia below the oesophagus encircling it with 

 nerve filaments ; respiration performed by direct contact of the 

 sea water with the vascular tissues of the brachia and mantle- 

 lobes ; reproducing by ova only. 



The above diagnosis includes all the characters common to the 

 class (which are not included in the definition of the type and 

 the subdivision to which this group belongs, according to my 

 views and those of much more eminent and competent naturalists) 

 which, after much study and reflection, I have been able to dis- 

 cover. 



I shall, further, assume that no characters not constituting a 

 large share, or possessing a preponderating value, in the defini- 

 tion of the class, or not contained in such an impartial definition, 

 shall be taken as proofs of the position of the class in a natural 

 system of classification. In this assumption I think I am sus- 

 tained by logic, common sense and the usual practice of natur- 

 alists. 



It will be noted that I have excluded from this definition any 

 allusion to peduncular or other attachment. I have not done this 

 without due consideration, but the fact that this character is not 

 even of family value, will amply justify the omission. The 

 Rhynchonellidce, Thecicliidw, Spiriferidai, Strophomenidw, Pro- 

 ductidce, Craniidce, and. even the Lingulidce, offer examples of 

 pedunculated and non-pedunculated, free and attached forms, 

 when the fossil forms are considered, and these comprise all 

 but two of the families of Brachiopoda admitted by Mr. David- 

 son in his well-known works. 



The oviducts differ within the same family from a simple per- 

 foration of the perivisceral tissues surrounded by distant papilla- 

 like elevations of the membranes, to a complex organ such as 

 exists in Waldheimia and Lingula. 



Some genera are undoubtably dioecious, and all may prove so, 

 but this is not yet fully determined. 



Seta? on the mantle edge are not constant characters in the 

 same family, or even in the same individual at different ages. 



The embryology is yet imperfectly known. A larva, supposed 

 to be that of a brachiopod, was figured by Fritz Miiller, but it 

 has never been confirmed, and still remains in doubt. The 

 researches of Prof. Morse (which agree with my own upon other 



