RAYMOND: SOME NEW ORDOVICIAN TUILOBITES. 293 



Several years ago Mr. A. G. Becker, while collecting in the ravine 

 of a small stream about two miles west of Clermont, Iowa, came upon 

 a slab of limestone on which were two specimens of the trilobite which 

 Slocum later described as Mcgalaspis heckeri. The outstanding feature 

 of this animal is the great elongation of the anterior portion of the 

 cephalon. The elongate triangular head-shield invited a comparison 

 with such asaphids as Mcgalaspis extenuata (Dalman), hence the 

 generic reference. 



No one has as yet been fortunate enough to discover an hypostoma 

 of this species, so that it is not possible to say definitely that M. 

 beckeri is not a Mcgalaspis, but that it is almost certainly not one is 

 indicated by the following considerations : — • 



1st. Nearly all the species of Mcgalaspis in the typical region in 

 northern Europe are found in the Lower Ordovician, only one or two 

 surviving till the Middle Ordovician, and none till the Upper Ordovi- 

 cian rocks were deposited. 



27id. Mcgalaspis is exceedingly rare in America, while isotelids are 

 common and highly variable. 



3rd. No hypostoma of the ogygiocarinid type has been found 

 in the Maquoketa. 



4th. The glabella of Mcgalaspis beckeri is not definitely outlined 

 and is long, while in all species of the true Mcgalaspis the glabella is 

 outlined and is relatively short. 



5th. The axial lobe of the thorax of M. beckeri is wider in propor- 

 tion to the total width than is that of any species of the true Mcga- 

 laspis. 



In consideration of the above, I make Mcgalaspis beckeri the type of 

 a new genus, Ectenaspis, the extended or stretched out character 

 of the cephalic shield suggesting the name. This genus seems very 

 close to Isotelus, and its derivation from Isoteloides through some 

 such forms as /. angusticaudus Raymond and Ectenaspis homalouo- 

 toides (Walcott) is quite probable. 



Ectenaspis beckeri is an exceedingly rare fossil in the lower part 

 of the Maquoketa (Upper Ordovician) in Fayette Co., Iowa. The 

 only other species which can now be placed in this genus is Ectenaspis 

 homalonotoides (Walcott). 



Isotelus annectans sp. nov. 



Isoteloides homalonotoides Raymond and Narraway (non Walcott), Ann. 

 Carnegie museum, 1910, 7, p. 52, pi. 16, figs. 9-11. 



