access to all the collections in our vicinity, and having frequently 

 visited the quarry at Braintree, and made a large collection of its 

 interesting treasures, I have thought the materials at my disposal suf- 

 ficiently large to enable me to make an accurate comparison of them 

 with the Paradoxides spinosus. Nor have I been limited in this com- 

 parison to the excellent figures and description given by M. Barrande 

 of the spinosus, but have been enabled to make the comparison 

 directly from the excellent specimens of that species which are in the 

 Museum of Comparative Zoology. After a long and careful com- 

 parison, I think I can venture to say that the Paradoxides Har- 

 lani is certainly a distinct species from the Paradoxides spinosus. I 

 will now lay before you the principal differences which have led me 

 to this opinion, and you can judge of its worth for yourselves. 



One of the first things that strikes us in examining the Paradoxides 

 from Braintree is its great size. Most of the specimens measure ten 

 and twelve inches in length, and some of them, as indicated without 

 doubt by fragments which I have found, must have measured at least 

 eighteen or twenty inches. In the " Systeme Silurien du Centre de 

 la Boheme," M. Barrande gives ten inches as the length of the largest 

 specimens of the Paradoxides sjnnosus, but in his more recent publi- 

 cations he says that he has found specimens in which the head is over 

 nine inches and a half in width. While this is the very largest speci- 

 men of the spinosus known, we have specimens from Braintree in 

 which the head measures about thirteen inches in width. 



The glabella of the Harlani is much wider in proportion to its 

 length than it is in the spinosus. What makes this especially apparent 

 is the difference which it produces in the anterior outline, making it 

 less oval, and giving the glabella a square appearance. The lateral 

 lobes of the glabella appear to have the same general shape as in the 

 spinosus, but I have not been able to determine their outline very 

 accurately. In no specimen, however, have I found the anterior 

 furrow of the glabella distinctly marked ; in fact, I have not been 

 able to satisfy myself of its presence. We can determine, however, 

 from the position of the other furrows, that if the anterior one was 

 present, its position must have been difierent from what it is in the 

 sjjinosus, and that, in connection with the squareness of the glabella, 

 would produce a material difference in the shape of the frontal lobe, 

 making it much narrower than it is in that species. 



It is perhaps in the cephalic limb that we find the most character- 

 istic differences. It is at least twice as broad, comparatively, in the 

 Harlani as it is in the sjyinosus. This great width of the Hmb alters 

 the exterior contour of the head to a great extent, causing it to present 

 the appearance of part of a very broad oval, instead of the more narrow 

 oval of the exterior contour of the head of the spinosus. It also alters 

 the direction of the facial suture, necessitates the changing of the 



