474 



HISTORICAL GEOLOGY. 



540. 



541-543. 

 543. 



Olenellus Gilberti Meek. 



Crustaceans. — Fig. 541, Leperditia der- 

 matoides; 542, Aristozoe rotundata; 

 543, Protocaris Marshi (^). Figs, from 

 Walcott. 



■ The Other Crustaceans pertain, to two still existing tribes of Entomostra- 

 cans, the Ostracoids and the Phyllopods. Figs. 541 and 542 represent 



Ostracoids from Wash- 

 ington Coiinty, X.Y. ; 



the dot in Fig. 541 



shows the position of 



the eye. Fig. 543 is 



the Phyllopod, Protoca- 

 ris Marshi Walcott, from 



Georgia, Vt. The shell 



may owe its flattened 



form to pressure. 



Doitbtful tracks. — 



The slender impressions 



of rounded surface that 



have been referred to 



seaweeds (Eucoids) may 

 be those of Worms or Mollusks. Another 

 kind, having a longitudinal impression along 

 the middle, called Cruziana (D'Orbigny) and 



Bilobites (De Kay), are regarded as the tracks of Annelids, Mollusks, or some 

 other Invertebrate. Fine Lower Cambrian examples are figured by Walcott. 



2. Middle Cambriai-t. 



The range of life in the Middle Cambrian is the same nearly as in the 

 Lower, but the species are mostly different, and in place of the genus Olenel- 

 lus among Trilobites, Paradoxides has special prominence. 



1. Sponges, Echinoderms. — 

 Remains of Sponges occur in 

 Nevada and New Brunswick. 

 The spicules. Fig. 544, are from 

 Nevada and are referred doubt- 

 fully to the Protospongia fene- 

 strata of Salter. Some simple 

 forms of Graptolites have been 

 found in New Brunswick. 



Cystoids are the prevailing 

 Echinoderms. A Nevada speci- 

 men (Fig. 545) has the usual 

 box-like body (whence the name 

 cystoid, from the Greek), with 

 unsymmetrically arranged arms 

 (mutilated in the specimen), and 

 the body-plates of irregular forms 

 (Fig. 545 a).. Plates of Eocystites were first reported from New Brunswick. 



544. 



545. 



545 a. 



Sponqe. — Fig. 544, Spicules; Protospongia feneBtrata(?) ; 

 545, Eocystites (?) longidactylus; 545 a, plates of portion 

 of body enlarged. Figs, from Walcott. 



