No. 3.] ZOOLOGY AND BOTANY. 361 



Lately published concerning the limbs of Trilobites, to say now 

 what bearing the facts described above may have upon the subject, 

 as lately discussed in The Journal of Science. But of one thing 

 I am satisfied, since I have examined the Tomocaris Peircei — 

 that Trilobites are not any more closely related to the Phyllopods 

 than to any other Entomostraca3, or to the Isopods. In reality, 

 the Trilobites are. like Tomocaris, a synthetic type, in which 

 structural feature of the Tetradecapods are combined with charac- 

 ters of Entomostracae and other peculiarities essentially their 

 own. 



The pygidium or abdomen of Tomocaris is very like the abdo- 

 men of the ordinary Isopods with an articulated oar attached 

 sideways and leaf-like respiratory organs upon the under side. 

 The whole pygidium is embraced between the last curved points 

 of the side of the thorax. Owing to these various combinations, 

 I would expect in Trilobites phyllopod-like respiratory appendages 

 under the pygidium only, and slender, articulated legs, with 

 lateral bristles under the thorax, so thin and articulated by so 

 narrow a joint as easily to break oflf without leaving more than a 

 puncture as an indication of their former presence. It is impos- 

 sible to study carefully the synthetic types without casting a side 

 glance at those natural groups, which, without being strictly syn- 

 thetic themselves, have nevertheless characters capable of throw- 

 ing light upon the whole subject. And in this connection I would 

 say a few words .of Apus and Limulus. If I remember rightly, 

 jMilne Edwards considers the shield of Limulus as a cephalothorax 

 in which the function of chewing is devolved upon the legs, while 

 he regards the middle region as an abdomen, and the sword-like 

 tail as an appendage sui generis. In the light of what proceeds, 

 I am rather inclined to consider the cephalic shield of Limulus as 

 a buckler homolo2;ous to that of the Trilobites, and the middle 

 region as a thorax in which the ring show unquestionably signs of 

 a division into lobes as in Trilobites. The tail would then answer 

 to the pygidium. Apus should be compared with the other 

 Crustacea, upon the same assumptions as Limulus. — Ever truly 

 your friend, L. Agassiz. 



— From the New York Tribune. 



Dredging in Lake Superior under the direction of 

 THE U. S. Lake Survey. — Extensive dredgings were under- 

 taken the past season in Lake Superior, from the U. S. steamer 



