STRUCTURE AND AFFINITIES OF TRILOBITES. 667 



the two eyes are placed on the back of the head wide apart. Here also there are no antenna, no 

 posterior lateral abdominal appendages, and besides no very distinct articulation to the sternum. 

 If the Bumastus of Murchison had a body of thirteen equal segments with short crustaceous feet 

 it would be a male Bopyrus, so close is the affinity ! The differences between a male and female 

 Bopyrus, such for instance as the presence of eyes in the former and the want of them in the 

 latter, may also induce us to fancy that similar differences may have possibly occurred between 

 certain male and female Trilobita, which from their prima facie difference of form are now placed 

 in distinct genera, although they may have truly belonged to one and the same species. Serolis 

 has been generally considered to come near to Paradoxides but as the former has got four well- 

 developed antennae with crustaceous feet, and the latter none, I am inclined to believe the relation 

 between them to be one of analogy rather than of immediate affinity. — Let us now turn to the En- 

 tomostraca. 



Dr. Buckland, following other authors, has compared the Trilobites with the genera Limulus 

 and Branchipus. With the latter genus, however, they obviously have no immediate affinity ; 

 although it may be well, by reference to Branchipus, to show that Crustacea can and actually do 

 exist, with soft membranaceous feet, such as Audouin and Brongniart suspected, and Goldfuss has 

 more lately asserted, to have been the feet of Trilobites. When, nevertheless, I take into considera- 

 tion the perfect manner in which the soft body of an animal referred to me by Mr. Murchison, 

 and by that gentleman called Nereites - Cambrensis, has left its impression in a slaty rock, I 

 confess I find it difficult to understand how the vestiges of legs in a Trilobite (if such legs ever 

 really existed) should not be more evident than Goldfuss has represented them in his plates. In 

 short, I consider the question of feet to remain still unsettled. At the same time I ought to remark, 

 that if the Trilobites were Crustacea, between Apus and Bopyrus, a fact I conceive capable of 

 demonstration, they must have been in possession of subabdominal, laminar, oviferous, appendages. 

 Now, no traces of such appendages remain, consequently we can easily understand how feet of a 

 similar membranaceous consistency may have disappeared in like manner. I may here observe, that 

 Brongniart is certainly wrong in imagining that the Ogygia Guettardi had oval oviferous bags 

 appendant to the abdomen like Cyclops, for what he considers to be such organs are more probably 

 the membranaceous margin of the abdomen, and, besides, Ogygia has no immediate affinity to 

 Cyclops. With reference to Limulus, its crustaceous, semilunar cephalothorax bears considerable 

 resemblance to that of certain Trilobites, such as the genera Ogygia, Asaphus, Paradoxides, &c. 

 In Limulus, we find reniform, compound eyes placed widely apart on the back of the head, and 

 consisting of peculiar facets. We find, also, an indistinct trilobed structure of the superior 

 abdominal shield. But then this is composed of a number of confluent segments, so as to appear 

 of one piece ; and, besides the two ocelli, the large crustaceous feet and cheliform antennas throw 

 Limulus far away from the Trilobites. We must, therefore, compare them with Apus and other 

 Aspidophora ; animals which, in my opinion, of all the Entomostraca, appear to come nearest 

 to the Trilobita, Here we have a large clypeiform shell, rounded in front, and posteriorly emar- 

 ginate, which forms a cephalothorax, on the back of which are situated three eyes. Of these, 

 the two largest are lunated, and obviously correspond to the eyes of Trilobita, although they are 

 placed proportionally much nearer each other. It is true they are simple, but so appear to have 

 been the eyes of Bumastus 1 (see PI. 7 bis, f. 3 c). The abdomen, divided into many distinct seg- 



1 The distinction between smooth eyes and granulose eyes does not seem to be of nrach importance in these 

 animals ; for among the existing family of Cymothoadce we not only see the males of some species with eyes 



