18 bulletin: museum of comparative zoology. 



Crustacea. 



Cryptolithus tessellatus Green. 



Cryptolithus tessellatus Green, Monog. N. Amer. trilobites, 1832, p. 73, pi. 1, 

 fig. 4. 



In Quebec, eastern New York, and central Pennsylvania, Crypto- 

 lithus tessellatus is one of the most common fossils in the lower part 

 of the Trenton, but in Ontario, Wisconsin, Minnesota, and Iowa it 

 has not yet been found. Even at Trenton Falls the species is so rare 

 that it has been found only a few times by local collectors, who form- 

 erly spent a great deal of time searching for rare fossils in that vicinity. 

 North of Trenton Falls and west of the Adirondacks it has not previ- 

 ously been reported. 



The specimens, which were all found in one layer about 100 feet 

 above the base of the section, seem to be quite typical, though all 

 rather small. In front of the girder there are two rows of pits, and 

 back of it at the sides there are three rows bordering the bases of the 

 lateral mounds. In front of the glabella there are three rows of pits. 

 Eye-lines are absent as is usual in the adult. 



