Raymond. — Isotelus gigas Dekay 



PLATE 2. 



Fig 1. — Basilicus harmndi (Hall). The imperfect cranidium which was the 

 type of Asaphus wisconsensis Walcott. From the Leray-Black 

 River at Newport, N. Y. X |. No. 47, M. C. Z., Walcott coll. 



Fig. 2-5. — Isotelus gigas Dekay. Young specimens in various stages of 

 growth, illustrating the change from the rounded to the pointed 

 pygidium and the shortening of the genal spines. From the 

 Trenton at Trenton Falls, N. Y. X |. No. 48, 38, 39, 40, 

 M. C. Z., Walcott coll. 



Fig. 6. — Isotelus iowensis Owen. An imperfect specimen from an unknown 

 locality in Iowa. To be compared with a young Isotelus gigas 

 from Trenton Falls (fig. 5) and with a young /. iowensis from the 

 same locality (Plate 3, fig. 2). X |. No. 420, M. C. Z., ? Sir 

 Charles Lyell coll. 



Fig. 7. — Basilicus harrandi (Hall). The specimen which was the type of 

 Asaphus romingeri Walcott. From the Leray-Black River at 

 Newport, N. Y. X f . No. 35, M. C Z., Walcott coll. 



