INVERTIOHRATR PALAEONTOLOGY. 255 



2. goniochasma. Meek. 



Shell transversely ovate-oblong; hiatus tunned bv a deep rectan- 

 gular notch in the anterior ventral margins ; umbonal sulcus and 

 corresponding internal ridge slightly oblique, and the latter finely and 

 obscurely crenate ; posterior internal ridge broad, deep, very oblique, 

 smooth, and not extending to the free margins. — G. Stimpsoni, 

 M. & H. 



3. xylophagella, Meek. 



Shell globose ; anterior hiatus formed by a large, deep, rectan- 

 gular notch in the anterior ventral margins; umbonal sulcus and 

 corresponding internal ridge descending vertically, the latter being 

 strongly crenate by little projecting points ; posterior internal ridge as 

 in the last, excepting that it is less oblique and placed in front of the 

 posterior umbonal slopes. — X. elegantula, M. & H. 

 At the time I proposed the last two of the above groups, I had no 

 knowledge of Mr. Gabb's genus Turnus, the description of which was issued 

 only a very short time previous to the publication of the Smithsonian list 

 containing my names. This list was in print at about the same time, but I 

 believe not issucd'for a month or six weeks after copies of the text of the 

 California report containing Mr. Gabb's name had Keen distributed ; con- 

 sequently, his name has priority of date. Since seeing his figure of the type 

 of his genus, and that of an intermediate species published by Dr. Stoliczka, 

 from the Cretaceous rocks of India, I am led, as already stated, to believe 

 that both of my proposed groups may be ranged as subgenera under the 

 same. It is still possible, however, that a better knowledge of these shells 

 may render it desirable to separate them more widely. The type of the 

 group Xylophagella, especially, will be seen to differ rather decidedly from 

 that of Turnus, not only in its deep rectangular notch or hiatus, but by its 

 short globose form and distinctly crenate internal anterior umbonal ridge. 

 This crenate character is not alone produced by the concentric furrows of 

 growth crossing the external furrows of the thin shell, as in the type of 

 Goniochasma, but consists of projecting points that leave deep little punctures 

 in casts of the interior. 



The type of tin' section Goniochasma has much the appearance of Mar- 

 tesia, and would have been ranged under that genus, were it not for the fact 

 that no traces of an accessory or dorsal valve have been seen in connection 





