BIONOMIC CHARACTERS OF MEROSTOMES 1029 



The young Limulus on hatching is a trilobitiform, free-swim- 

 niing, commonly meroplanktonic organism without caudal spine 

 (J. S. Kingsley). 



Modern Limulus is restricted to the eastern shores of America 

 and Asia. A Tertiary species (L. decheni) is known from the 

 Oligocenic brown coal of Teuchern, near JMerseburg, in Saxony, 

 an occurrence scarcely suggestive of marine habitat. A marine 

 species (L. zvalchi) is abundant in the lithographic slates of Ba- 

 varia, associated with land forms, however. A small species occurs' 

 in the Bunter Sandstein of the Vosges, a formation chiefly of ter- 

 restrial (river) origin, and suggesting that Limulus in the Trias 

 was still a river animal. This was most probably true also of 

 Protolimulus. which occurs in the Chemung delta deposits of 

 Pennsylvania. The Carbonic Xiphosurans, Prestwichia, and Beli- 

 nurus were undoubtedly fresh-water (river) organisms, occurring 

 in the non-marine coal deposits. Cyclus, on the other hand, is 

 found in the interbe.dded limestone of the Coal Measures, as well 

 as in the Coal Measures themselves. The habitat may have been 

 marine, but not necessarily so, since these carapaces could easily 

 have been washed from the land. 



Altogether it seems as if the early Xiphosurans were river-living 

 animals, venturing perha])s occasionally into the sea (euryhaline) 

 and assuming their marine habitat in the Mesozoic and modern 

 times. 



The Synxiphosurans may have been partly marine and partly 

 fresh water, The Upper Cambric Aglaspis suggests their derivation 

 from the trilobites. This occurs in the St. Croix sandstone of 

 Wisconsin, a terrestrial deposit reworked by the sea. The Siluric 

 genera Neolimulus, Bunodes, Hemias])is, and Bunodella occur in 

 deposits which are partly marine and partly of delta type. It is 

 not improbable that most of them were derived from the land- 

 waters and buried in the sea margin deltaic deposits. The possi- 

 bility of a marine character for some can, however, not be denied. 

 Pseudoniscus, on the contrary, in America occurs in the Pittsford 

 black shale deposits, which are most suggestive of influx of fresh 

 water, and hence a non-marine habitat is indicated. The European 

 species are from Oesel and their real habitat is doubtful. (O'Con- 

 nell-20. ) 



The Eurypterida have generally been considered marine, but 

 the elaborate study of the habitat of these organisms made by Miss 

 O'Connell (20) points unmistakably to a non-marine habitat of 

 these merostomes since j)re-Cambric time. The majority of forms 

 occur in rocks not explainable as normal marine sediments, but as 



