8UB-CLA88 I 



TRILOBITA 



Most of the recent advances in tin- knowN-d^r of Tiilol.itr stnn-Mnr ha\.- 

 come from the study of nuinrmn> very prrfn-ily pn-i-r\rd .-.pi'i-im. 

 Trio /Hi ru.< /////', (Irern, hom tin- I'tira Shite (Ordovi<-ian). m-ar Koin> 

 York. Undoubted antrnnar in this form wnv discovered ly \';iliant, ami tii>t 

 announced by Matthew in 189.'$. Subsequently a series of papn 

 published by Beecher on the detailed structure of this Trilobite, which is now 



Fi.:. 12C.7. 



Trio rtltrus Becki, Green. Utica Slate (Ordovician) ; Rome, New York. A, Dorsal, ami /;, V.-ntral aspect, 

 2/j (after Beecher). 



the best known of any species, and necessarily forms the basis of much of the 

 following summary of ventral organs. 



In the median line anteriorly, there is first the hypostoma or upper lip, at 

 the end of which, and opening obliquely backward, is the mouth (Walcott, in 

 Calymmene). In Trwrtlinix the lower lip, or metastoma, is a convex arcuate 

 plate, just posterior to the extremity of the hypostoma. At the angles on 

 either side are two small elevations, or lappets. 



Paired Appendages. All segments of the cranidium, thorax, and pygidium, 

 except the anal segment, carry paired appendages, which are all biramous save t In- 

 anterior pair. The anterior antennae, or antennules, are attached at the sides 

 of the hypostoma, and consist of a simple, many -jointed flagellum (Fig. 1267). 



