114 IOWA GEOLOGICAL SURVEY 



Spines belonging to the typical species, M. peracutus New- 

 berry, occur in the Columbus and Delaware limestones of Ohio, 

 and the equivalent Onondaga limestone of New York State. M. 

 sulcatus (Plate III, Fig. 4) is more widely distributed in rocks of 

 the same age, and its persistence at different levels (Logan's 

 Divisions 1 and 6) of the Gaspe series* in eastern Canada ap- 

 parently indicates a migration northward beyond the confines 

 of the Appalachian basin. M . longaevus is a Hamilton species, 

 occurring typically in western New York, but may be repre- 

 sented also by a few doubtful fragments in the Hamilton lime- 

 stone of Milwaukee, Wisconsin. No indications of this genus 

 have been discovered as yet in the Iowa Devonian. 



Genus gyracantms Agassiz. 



The paired fin-spines of this genus have not been found asso- 

 ciated with other parts of the skeleton in any instance thus far 

 reported, but their position and mode of attachment are readily 

 to be divined from analogy with the remarkable Australian form 

 described by Smith Woodward under the name of Gyracanthides 

 murrayi. Two Devonian species of Gyracanthus are already 

 known from the rocks of this continent: G. incurvus Traquair, 

 from the Lower Devonian of Campbellton, New Brunswick; and 

 G. shertvoodi Newberry, from the Chemung-Cat skill of New 

 York and Pennsylvania. An illustration of the latter form is 

 given in Plate III, Pig. 1. A notice of a third species immediately 

 follows. 



Gyracanthus primaevus, sp. nov. 

 (Text-fig. 17) 



Pounded upon a unique fin-spine of relatively small size, the 

 total length being probably not more than 8 cm, and maximum 

 width in antero-posterior direction 0.75 cm. Slender in form and 

 of graceful proportions, the spine is much laterally compressed, 

 regularly and rather strongly arched, and gradually tapering to 

 an acute apex. The ornamentation consists of numerous fine 



* Geology of Canada, 1863, p. 395.— Paheozoic Fossils, 1874, part 1, 2, pp. 3, 4. 

 -Lankester, E. R., Geol. Mag. 1870, 7, p. 398, text-fig. 3.— Clarke, John M., 

 Evidences of a Coblenzian Invasion in the Devonic of Eastern America. A. von 

 Koenen's Festschrift, 1907, p. 359. Idem, Earlv Devonic History of New York and 

 Eastern North America. Mem. N. Y. State Mus. 9, 1908, p. 76 ff. 



