44 



these animals. The type here represented is the species 

 7 riarthrus Becki from the Utica Slate, near Rome, 

 N. Y. 



The model of the upper, or dorsal, side presents the 

 carapace of the animal with its divisions of ( i ) cepha- 

 lon, or head; (2) segmented thorax, or body; and (3) 

 pygidium, or tail. The walking and swimming legs are 

 seen extending ovitward from beneath the edge of the 

 carapace. In front is a pair of long, slender, jointed 

 antennules. 



The model of the lower, or ventral side, shows the 

 details of the appendages more completely. Each seg- 

 ment of the body has a pair of biramous or branched 

 limbs. One series of legs is adapted to crawling, and 

 the other is provided with fringes, and forms a series 

 of swimming appendages. At the origin of each branched 

 limb there is a process extending obliquely backward to- 

 ward the center. These are called gnathobases, and on 

 the head they become jaw-like organs. 



The large plate between the bases of the antennules is 

 the upper lip, or hypostoma. Just below it is a smaller 

 plate, forming the lower lip, or metastoma. The mouth 

 is situated between the two. 



The models are enlarged two diameters, and are made 

 of various materials, as colored plaster of Paris, emery, 

 and copper. 



10. Developmental Series of Graptolites and Pteropods 



FROM the Lower Utica Shale at Dolgeville, 



N. Y. 



Exhibited by Dr. Rudolph Ruedemann, Dolgeville, 



N. Y. 



a. Specimens illustrating development of Diplograptus 



pristls Hall and D. Ruedematini Gurley. (Report 



State Geologist, N. Y., for 1894 [in press] ). 



Nos. I and 2 are two well-developed stellate groups of the two 

 species. 



