158 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



Tuzoia (pi. 33, fig. 2), also approximates in pattern and size that of 

 Nehaliopsis typica Sars.^ 



The merostomes Sidneyia,^ Amiella^ Habelia (pi. 29), Molaria 

 (pi. 29), and Emeraldella (pi. 30), have a compact cephalic shield 

 and well-defined thoracic and abdominal segments and telson that 

 are similar in character to the dorsal shield of the trilobite. 



Labnim. — The labrum or hypostoma of Sidneyia' Emeraldella) 

 (text fig. 8, p. 204), and Marrella (pi, 26, fig. 2) is clearly shown in 

 a number of specimens, also that of Burgessia (pi. 27, fig. 2), but 

 in the other species it has not been seen nor has the lower lip 

 (labium or metastoma) been observed in any species. 



Segmentation. — The following table gives the number of cephalic, 

 thoracic, and abdominal segments so far as known. The eyes are 

 considered as representing a segment, which gives six segments in 

 the cephalic region. 



Table of Cephalic, Thoracic, and Abdominal Segments. 



Genera. 



BRANCH tOPODA. 



Opabinia 



Leanehoilia 



Yohoia 



Bidentla 



Naraoia 



Burgessia 



Anomaloearis 



Waptia 



MALACOSTRACA. 



Hymenocaris 



TRILOBITA. 



Marrella 



MEROSTOMATA. 



Sidneyia — 



Habelia 



Emeraldella 



Molaria 



6 



6?2 

 3 



6? 



1 All that have been seen on imperfect specimens. 



2 The eyes are considered in this table as representing a cephalic segment. 



In the table the telson has been included as an abdominal segment 

 and the caudal rami are considered as attachments of the terminal 

 segment. 



Appendages. — So far as can be determined from the specimens 

 now available for study the normal number of cephalic appendages 



"Challenger Rept., 1887, Vol. 19, Pt. 56, pl. 3, figs, i, 5. and 6. 

 "" Smithsonian Misc. Coll., Vol. 57. iQio, pis. 2-7. 

 'Idem. pl. 5. 



