ZOOLOGY. 431 



ARTHROPODS. 



MEROSTOMES. 



Trilobita. 



Ford (S. W.). Embryonic Forms of Trilobites from the Piimordial Rocks of Troy, N. 



Y. Am. Journ. Sc, (3,) v. 22, p. 250-259. 

 Walcott (C. D.). The Trilobite : New and Old Evidence relating to its Organization. 

 Bull. Mus. Comp. Zool., v. 8, p. 191-230, witli G pi. 



Xipliosura. 



Jonsset de Bellesme. Observations sur les fonctions de Fappendice caudal des Limules. 



Ann. Scienc. Nat. (6), v. 2, Art. No. 7. (5 p.) 

 Lankester (E. Ray). Limulus an Arachnid. Quart. Journ. Mic. Sc, n. s., v. 21, pp. 

 584-548, 609-649, pi. 28-29, July and Oct., 1881. 



Belations of the Merostomes. 



The Merostomes, i. e., the Horseshoe Crabs of the present epoch 

 and their ancient relatives, as well as the Trilobites, have been almost 

 universally considered, until within the last few years, as true Crus- 

 taceans. As long ago as 1829, however, an eminent French anato- 

 mist— Straus Durkheim — maintained that Limulus belonged rather to 

 the Arachnids, and was the type, in that class, of a peculiar order, 

 which he named " Gnathopodes." The Arachnids, for him, were char- 

 acterized by the legs abutting on a common sternum, the presence of 

 an internal cartilaginous sternum, and the absence of antennae. Al- 

 phonse Milne-Edwards i)roposed to isolate the group as an intermediate 

 form between the Crustaceans and Arachnids. Claus and Packard 

 considered the grouj) to be one of i^rimary importance within the Crus- 

 taceans, the Horseshoe Crab and its allies representing a subclass in 

 contrast with all the other representatives of the class. 



Prof. E. Eay Lankester has recently discussed the gross morphology 

 and relationships of these most gigantic of articulates in the Quarterly 

 Journal of Microscopical Science, and presented quite a complete and 

 well-digested analysis of their characters compared and contrasted with 

 those of Arachnids and Crustaceans. A detailed comparison is insti- 

 tuted between Limulus and Scorpio, segment for segment, and the 

 results thereof are summarized in very convenient form, in tables, for 

 Linuilus on one page, and Scorpio on the opposite, exhibiting in several 

 columns the characteristics of the segments from the first to the eight- 

 eenth, as to (1) the Tergites, (2) the Sternites, and (3) the Appendages. 

 The differences between the forms thus specially compared are great in 

 some respects, although generally less than those which would be appar- 

 ent on a comparison between Limulus and any true Crustacean. The 

 hiatus intervening between the two is, however, to a considerable ex- 

 tent bridged over by theEuryptorina of the Pahuozoic epoch. Inasmuch 

 as the close aCtinity of the Eury[)ieriiui to the Limulids is now univer- 

 sally admitted, that which is relevant to the former is applicable to the 



