27(5 C. SQHUCHERT — LOWER HELDERBERG— ORISKANY FORMATIONS 



or subgenera : Homalonotus, Bronteus^ Dalmanites, Proboliunt, OdontocheUe, 

 Phacops, Acidaspis, TAchas, Cordania, Proetus, and Cyphaspis. This enu- 

 meration fails to present some of the must characteristic fossils of the 

 American Siluric, as Bumastu8 } Encrinurus, Sphaerexochus^Cheirurus^Calym- 

 mene, and particularly Tllmnus so prolific in species. Of the abundant 

 Siluric eurypterids and oi jOeratiocaris^ none occur in the Helderbergian. 

 On the other hand, the Helderbergian trilobites of the genera Bronteus, 

 Phacops, Addaspis, and Cordania have decided Devonic affinities, while 

 Dalmanites (Odontocheile) is rather Devonic in development, although 

 there are related species present in the Siluric. Calymmene again ap- 

 pears in the Onondaga. 



The hrachiopods may also be regarded as of prime importance because 

 of their wide distribution, abundance, and specific differentiation. In 

 the Helderbergian, there are no less than 137 species. A Devonic aspect 

 is indicated in the large size attained by most of the species, and the 

 abundant specific development of the subgenera Rhipidomella and Dal- 

 manella. Christiania and Leplsenisca are genera in which the shell is an- 

 chored directly to some foreign object, but this feature is unknown in 

 earlier faunas, and becomes more and more marked in the later Devonic 

 and Carbonic. CJionostrophia is introduced in the Helderbergian and is 

 continued into the Middle Devonic. Stropheodonta and Strophonella, 

 which are represented by few and generally small species in the Siluric, 

 are here present in great force and large size, recalling strongly the Mid- 

 dle Devonic. As to size and abundance, the same is true of the Rhyn- 

 chonellas, while IAssopleura and Eatonia are unknown in the Siluric. 

 Gypidula galeata and Anastrophia verneuili are good Siluric stragglers, but 

 also denote a younger age in their greater size. The Spirifers, while in- 

 dicating the Siluric, point without exception to post-Siluric age in their 

 larger size and abundance; a characteristic Devonic aspect not being- 

 attained before the later Oriskany. The Retzias betoken post-Siluric age 

 in their size and greater specific differentiation, while the finely plicated 

 form of Middle Devonic time has here its first appearance in Parazyga. 

 Meristella is unknown in the Siluric, but in the Helderbergian there is 

 an abundance of this genus, and some of the forms have almost specific 

 identities in the Middle Devonic. However, the most decided Devonic 

 brachiopod facies is in the loop-bearing genera Rensselseria, Trigeria, and 

 Cryptonella. Not one of the Terebratulacea is known in the Siluric, while 

 in the upper portion of the Lower Devonic, both in America and Europe, 

 the genera Rensselseria, Meganteris, and Trigeria have a size rarely attained 

 by any subsequent terebratuloids. 



On the other hand, of the characteristic Siluric trimerelloids of the 

 genera Dinoholas, Rhinobolus, Monoinorella, and Trimerella, not one is 

 present. Of the strophomenoids, Plectambonites, Slrefitis, Mimulus, and 



