128 G. F. MATTHEW : ILLUSTRATIONS OF 



shield ; it was evidently flexible, and did not perform the functions of a spine in protecting 

 the animal when the fehield and thorax were folded together. 



The angles of the head-shield in Soleuoplenra had but little more protection ; in this 

 genus, a point, small and weak, projected backward and outward from the genal angle. 

 Ptychoparia is the only genus among those described in this article in which a true genal 

 spine has actually been found attached to the test. 



To sum up these observations on the comparative standing of the several genera des- 

 cribed in tliis article, as derived from a study of the development of the head-shield of the 

 young in the species wherein this is known, the following comparative statement is given, 

 the genera which shew the most primitive features being named first : — 



Eyelobes. — EUipsoceplialiis, Agraulos, Liostraeus, Ptychoparia, Solenopleura. 

 Dorsal Suture — Agraulos, EUipsooephalus, Liostraeus, Ptychoparia, Solenopleura. 

 Glabella. — Ellipsocephalus, Solenopleura, Ptychoparia, Liostraeus, Agraulos. 

 Anli-rior Margin. — Ellipsocephalus, Agraulos, Liostraeus, Solenopleura, Ptychoparia. 

 Occipital Ring. — Ellipsocephalus, Agraulos, Liostraeus, Ptj'choparia, Solenopleura, 

 Movable cheek. — Ellipsocephalus (?), Liostraeus, Solenopleura, Agraulos (?), Ptychoparia. 



The sum of these characters give the above genera the following standing : — (1) Ellip- 

 socephalus, (2) Agraulos, (3) Liostraeus, (4) Ptychoparia, (5) Solenopleura. 



This is nearly the order in which, so far as it is known, they appeared in the St. John 

 Basin ; except that Agraulos proper (the flat-headed form) is not known to have appeared 

 until after the genera which are named after it. 



L— ellipsocephâlidjî:. 



ELLIPSOCEPHALUS, Zenker. 



In all coiTntries where there is a valid representation of the earliest types of the 

 Primordial fauna, this genus is present. It is of interest to the naturalist, not only on 

 account of its antic^uity, but also because of its early extinction, for if we except Ellipso- 

 cephalus circulus, Brogg., and E. German, which are only distantly related to the early typical 

 forms, the genus characterises the oldest layers of the Cambrian formation, and there is a 

 close similarity between all the early species in the form of the head-shield. Besides the 

 type of the genus E. Hoffi, Scholth., of the Primordial zoue, in Bohemia, there is a number 

 of species described from the lower Paradoxides beds of Sweden.' G. Linnarssou evidently 

 depends upon the distinctness of the occipital ring to distinguish the Swedish species 

 from those of Bohemia, but in my examples of E. Hoffi (test nearly mature) from Bohemia, 

 the neck furrow is as distinct as in the Swedish specie?. 



The differences between the Swedish species are partly in the sculpture of the surface, 

 partly in the distinctness or obscurity of the glabellar lobes, and in some species in the 

 number of segments in the thorax. The four Scandinavian species are very near each other ; 

 or, in other words, are critical species. In the forms which are foand with us in the species 

 Conocorijphe Baileyi, or in the varieties which are grouped in this article under Liostraeus 



' Om faunan med Paradoxides Oëlandicus, Stockholm, 1877, p. 366. 



