; TRENTON CONGLOMERATE OF RYSEDORPH HILL 41 



ziTTELocERAs Hyatt 

 Zitteloceras hallianum d'Orbigny sp. 



Cyrtoceras hallianum d'Orbigny. Prodr. de pal. 

 1850*! 1:1 



Oyrtoceras lamellosum Hall. Pal. X. Y. 1817. 1 :193 



In tlie black limestone, fragments of C y r t o c e r a s hallia- 

 num were found with the undulating squamous lamellae 

 characteristic of this species. Hall knew this species only from 

 the lower part of the Trenton limestone at Middleville, and later 

 collectors do not mention it. Dr Clarke reports it from the 

 Black river beds of Wisconsin and Minnesota. (Group 5) 



CRUSTACEA 



TRETASPis McCoy 



Tretaspis reticulatus sp. nov. 



PI. 3, fig. 11, 15-20 



Several pebbles of black compact limestone were found to 

 be filled with a*trinucleid, representing the genus Tretaspis 

 which is new to this hemisphere. The specimenis, about 20 of 

 which were obtained, occur in association with A m p 3' x h a s t a- 

 tus, Illaenus americanus, Ceraurus pleure- 

 X a n t h e m u s , S p h a e r c r y p h e major, Cypha<spis and 

 plates of a Glyptocystites. 



Diagnosis. Cranidium subrectangular to semicircular in out- 

 line, the former irt younger specimens; length to width as 3:8; 

 frontal margin slightly rounded to nearly straight. Glabella 

 pyriform with the anterior part spheric, abruptly widening and 

 rising above the neck of the glabella; frontal part reaching to and 

 slightly overhanging the frontal border; posterior part of glabella 

 narrow, angular and provided Avith a median crest extending 

 from the occipital ring to about the middle of the frontal lobe, 

 where it ends with a tubercle. There are three pairs of deep pits 

 or fossae; the first small, deep and round, well up the tumid part 

 of the glabella; the second broad and oval extending obliquely 

 forward from the dorsal furrow; the third deep, transverse 

 impressions situated a little anteriorly of the occipital furrow. 



