BIBLIOGRAPHY OP PAL/EOZOIC ORLISTACE\ 119 



WALCOTT (Charles P.)— Continued 



Albertella n. genus, Genotype A. Helena n. sp. 



The genus should be compared with the genus Zacanthoides. The ceplialons of the 

 two genera are generically the same. Tlie thoracic segments are the same tyj^e, but the 

 third or fourth segment of the thorax of Albertella is extended into long pleural spines, 

 and the thorax has seven instead of nine segments as in Zacanthoides. The p\gidium 

 has one pair of spines instead of many spines, as in Zacanthoides. 



Albertella Boszvorl/ii n. sp. 



Oryctocare new genus, genotype (). Geik'tei n. sp. 



The cranidium of the cephalon of tliis genus is much like that of Oryctocephalus, 

 but the thorax and pygidium are unlike. The pleurae are of the Oleniis t\ pe, while 

 ihe pygidium is broad and of the Bathyuriscus type. 



Zacdtilhoides ulalioensis n. sp. Neolenus 'uillalii.< n. sp., A'. intermeJiiis n. sp., A'. 

 iiitermeJius pugio n. variety, M. super hus n. sp. 



lialliyuriscus ornatus n. sp. 



^liddle Cambrian ]\lerostoniata. 



Smithsonian Mis. Coll., vol. 57, No. 2, Washington, 1911. 



In this paper two genera, Sidneyia and Amiella, are described. 



S'ldney'ia inexpectans Wale. A miella ornatn ^^'alc. Xeole/ius .wrratits Rominger. 

 Belthis Danai Wale. 



The new genera are placed in a new suti-order I.imulava of the order Eurypterida. 



Sidneyia with its four pairs of cephalt>-tlioracic api^endages and simple antennae 

 approaches the Trilobita, wliich has a similar scheme of cephalic appendages. 



('aml)rian Geolooy and PaltT?ontology, No. (5. Olenelhis and 



other genera of the j\Iesonacida\ 



Smithsonian Misc. Collections, vol. 53, No. 6, 1910, pp. 231-422, Pis. 22. 

 The author under the family Mesonacidae places: 



1. Nevadia n. gen. genotype N. IVetksi n. sp. 



In the type of this genus tlie posterior 11 segments ]ia\e onl\ the axial lobe and a 

 spinose continuation on each side. Tiie spinose extensions of the posterior segments 

 are proportionally much rounder and smaller than those of the anterior 17 segments. 

 The pygidium is small without pleural lobes and trans\erse furrows. 



2. Mesonacis: This form is essentially the same as Elliptocephala, but it has an 

 enlarged third segment in the adult, an<l a strong spine on the fifteenth segment. 



The species referred to Mesonacis are M. vrrmontana Hall, .1/. Mickivitzi Schmidt, 

 and M. Torrelli Moberg. 



Elliptocephala Emmons, genotype E. asaplioiJes Emmons. 



In the genus the posterior five segments are more highly developed than ihe primi- 

 tive segments of Nevadia, but not as much so as the segments anterior to them. 



Callavia Matthew, genotype Olenellus (Ilolm'ia) hrUi^iieri Walcott. 



This genus w-as proposed by Matthew, .'\m. (.eol., vol. 19, p. 397, 1897, for O. 

 hriii^i^rri and (). callavii Lapw., on acccount of the ijlabella differing from that of 

 Olenellus (Ilolm'ia) Kjerulfi. 



Callavia has a trace of the constricted pleurae of the posterior portion of the thorax in 

 the tvyo last segments. The broad thorax of Callavia with the falcate extensions of 

 the pleurae are unlike the narrow thorax of Holmia with its spinos pleural extensions. 



The glabella of Callavia is narrower and more primitive, and its intergenal spine is 

 less primitive. The pleural furrow of Callavia is narrow and oblique, like that of 

 Paradoxides, while the pleural furrow of Holmia and W^aiuieria is broad and straight. 



The segments of Callavia appear to be nearer to I''lliptoceiihala, than to those of 

 Holmia. 



