ib2 Observations on Trilobites. 



nal furrows into three parts ; we have indicated rudiments ot 

 a similar division in the specific description of the /. gigas. 



2. The description and figure of a fossil Trilobite, as given 

 by Parkinson in the third volume of his Organic Remains, 

 represents an animal intermediate between the recent Limulus 

 and our Trilobite. The head is imperfect. " The body (ab- 

 domen) has five transversal plates ; its sides go off directly 

 from the head, and meet speedily at an obtuse angle, &,c." 



A direct comparison of the recent Limulus with the Isotelus, 

 will furnish us with additional arguments in favour of their 

 near resemblance. The former animal is often taken in great 

 abundance along our shores, and when thus taken, is im- 

 mediately turned over on its back to prevent its escape j 

 in this position they are well-known to inflect their abdomen 

 upon the buckler. And this seems to be an approximation 

 towards similar habits of the Trilobite. 



4. The lunated transparent cornea, which may be seen in 

 many of the Trilobites in the Cabinet, bears a very strong re- 

 semblance to that of the Limulus. In young individuals of the 

 L. polyphemus, the eyes are partly raised on the exterior 

 spines of the first row, these, together with the other spines, 

 are effaced by age, and the eyes then become nearly continu- 

 ous with the surface of the buckler. This fact may stand as 

 an answer to one of M. Latreille's objections. 



On the anterior edge of the buckler, a raised rim or bor- 

 der is equally observed in the Isotelus and Limulus, and the 

 rudiments of two longitudinal depressions on the buckler of 

 the Limulus, are very apparent. 



6. The upper surface of the abdomen of this latter animal, 

 exhibits seven foramina, connected beneath with as many thin 

 membranous gilts. We have only to suppose these foramina 

 extended transversely across the abdomen, and we have at 

 once the lateral lobes of the Trilobite. 



Finally, the analogy between the Trilobite and Limulus, 

 derives additional support from the following circumstances. 



