1 8 VTHE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



men, and it is also referred to by Wahlenberg (1821, pi 39), Brongniart (1822, p. 42), 

 Dalman (1828, p. 73), and Angelin (1854, p. 46). 



Audouin (1821) seems to have been the first naturalist with sufficient knowledge of 

 the Arthropoda to be competent to undertake the study of the trilobites. He concluded that 

 the absence of ventral appendages was probably a necessary consequence of the skeletal 

 conformation, and thought if any were discovered, they would prove to be of a branchial 

 nature. 



Wahlenberg (1821) in the same year expressed his belief that the trilobites were nearly 

 allied to Limulus and in particular tried to show that the trilobites could have had masti- 

 catory appendages attached about the mouth as in that modern "insect" (p. 20). Wahlen- 

 berg was also the first to describe an hypostoma of a trilobite (p. 37, pi. I, fig. 6), but 

 did not understand the nature of his specimen, which he described as a distinct species. 



Brongniart (1822, p. 40) devoted five pages of his monograph to a discussion of the 

 affinities of trilobites, concluding that it was very probable that the animals lacked antennae 

 and feet, unless it might be that they had short soft feet which would allow them to creep 

 about and fix themselves to other bodies. 



Schlotheim (1823) thought that the spines on Agnostus pisiformis were segmented 

 and compared them with the antennae of Acarus. 



Stokes (1823) was the first who, with understanding, published an illustration of the 

 ventral side of a trilobite, having figured the hypostoma of an Isotelus. He was followed 

 in the next year (1824) by Dekay, who also figured the hypostoma of an Isotelus, and 

 added some observations on the structure of trilobites. The researches of Barrande, Novak, 

 Broegger, Lindstroem, and others have dealt so fully with the hypostoma that further refer- 

 ences to that organ need not be included here. 



Dalman (1826, 1828) reviewed the opinions of his predecessors, and thought it not 

 impossible that organs of mastication may have been present under the head shield of the 

 trilobite as in Limulus (1828, p. 18). In this he of course followed Wahlenberg. 



Goldfuss (1828) figured sections of Dalmanites hausmanni, Phacops macro phthalina, 

 and Calymcnc tristani, which remind one of some of Doctor Walcott's translucent slices. 

 So far as one can judge from the illustrations, it is probable that what he took for limbs 

 were really fragments of other trilobites. Such is certainly the case in his figures 9 and 

 10, where a number of more or less broken thoracic segments are present. The section of 

 Encrinurus punctatus shown in figure 7 may possibly exhibit the position and folds of the 

 ventral membrane beneath the axial lobe, and also, perhaps, the appendages. His figures 4, 

 5 and 8 show the hypostoma in section. 



Pander (1830) described the hypostoma in greater detail than had been done by previ- 

 ous authors, but otherwise added nothing to the subject. 



Sternberg (1830) thought he had individuals showing appendages, but judging from 

 his poor figures, he was deceived by fragmentary specimens. 



Green (1839 A, B, C) described specimens of Phacops from Berkeley Springs, West 

 Virginia, which had the hypostoma in position, and appear to have had a tubular opening 

 under the axial lobe. While appendages were not actually present, these specimens sug- 

 gested fairly correct ideas about the swimming and breathing organs of trilobites. They 

 were similar to the ones which Castelnau obtained, and all were perhaps from the same 

 locality. 



It is not worth while to do more than enumerate the other authors of this period : 

 Hisinger 1837, Emmerich 1839, Milne-Edwards 1841, for they all shared the same views, 

 and added nothing to what was already known. 



