LARVAL STAGES OF TRILOBITES 175 



features of the glabella. The specimen seen in figure 4 rep- 

 resents a late larval stage (paraprotaspis), as shown by the 

 transverse form of the cephalon and the large size of tlie 

 pygidium. 



Proetus parviusculus Hall ; Plate IV, figures 5, 6, and 7 ; 

 Utica slate, near Rome, New York. Two larval stages of 

 this species have been found. The younger (figure 5) is 

 smooth, broadly ovate, .72 mm. long, and widest in front ; 

 axis distinctly annulated, cylindrical on the cephalon, tapering 

 on the pygidium ; eyes nearly transverse to the axis, very 

 large and prominent, situated on the anterior margin, sepa- 

 rated only by the axis. The specimen represented in figure 6 

 is in the parapi'otaspis stage, and measures .96 ram. in length. 

 It shows an advance over the other in its size, its larger pygid- 

 ium with grooved pleura, and the beginning of the recession 

 of the eyes. 



The adult of this small species is shown in outline enlarged 

 two diameters, in figure 7. The principal changes from the 

 larva which should be noticed are : the loss of the four ante- 

 rior annulations of the glabella, the neck segment being the 

 only one wholly defined, although the basal lobes represent 

 remnants of the next anterior; the translation of the eyes 

 backward as far as the pleura of the neck segment, and the 

 change from a transverse to a parallel position with respect 

 to the axis. 



In the original description of this species,^^ no mention was 

 made of fine undulating strise ornamenting the entire dorsal 

 surface of the test, nor of the basal lobes of the glabella. 

 Both these features are present in the type specimen, which is 

 from Cincinnati, Ohio, as well as in all the specimens from 

 the Utica slate, near Rome, New York. With these additional 

 characters the species is very closely related to Proetus deco- 

 rus Barrande. 



Dalmanites socialis Barrande ; Plate IV, figures 8-11 ; from 

 the Ordovician of Bohemia; after Barrande.^ A nearly complete 

 series of the growth stages of this species is given by Barrande. 

 The earliest, or anaprotaspis, stage found (figure 8) exhibits an 



