1 91 6. No. JO. THE LOWER CAMBRIAN HOLMIA FALXA. 



Sireniiclla through a series of stages to the most typical Middle Cambrian 

 Ellipsoccphalus forms; but it must be emphasized that we are still unable 

 to constitute certain lines of development, but merely stages in the same. 



The difterentiations that are here met with are mainly the following: 



1. The cranidium changes its form b\' degrees, the contours of the 

 glabella becoming more and more parallel, finally being slightly con- 

 tracted between the eye-lobes, whilst anteriorly it becomes more and 

 more pointed. 



2. The free cheeks become rounded without corner spines. 



3. The number of segments is reduced, and the latter by degrees lose 

 dieir pleural spines. 



4. The pygidium becomes short and extended. 



The Bohemian province possesses yet another Middle Cambrian Ellip- 

 socepliahts form, viz. El. German Barr. Besides its considerable size, the 

 latter is distinguished by its flat, extended cranidium, and its comparatively 

 broad free cheeks, which posteriorly end as long genal spines. The form 

 of the glabella is markedly Ellipsoccplmlidc. The segments, numbering 14, 

 are flatter and less geniculated than usual, and the pygidium is short and 

 broad. In other words it has a tlatly extended main form, which I assume 

 has developed along a special line from Strcnuclla-Wk^ original forms. 

 This is also shown by the long genal spines which in all the other Middle 

 Cambrian Ellipsocephalns species have been reduced. The interesting 

 Norwegian Ellipsoccphalus c'dxhIhs Brogger- from the Paradoxides Forch- 

 hammeri-zonç: at Krekling exhibits a certain resemblance to the Bohemian 

 form. Unfortunately the two specimens found are very much compressed 

 and somewhat indistinct, so that several characters cannot be determined 

 with certainty. The almost Harpes-like form of the head indicated a fossorial 

 mode of life in the mud at the bottom of the sea, and in this respect it 

 reminds one more of certain species of the genus ,'4graidos, particularly 

 the younger stages of the A^r. diffonuis series. 



As the course of the facial sutures behind the palpebral lobes also 

 agrees in all respects with that of Agrauhs and differs from that of 

 PJllipsoccp/ialus, I am inclined to regard it as belonging to the former 

 genus. It would then be considered as a remarkable differentiation ot the 

 richly varying Agraidos diffonuis series. 



' J. F. PoMPECKj: Die Fauna des Cambrium von Tejrovic und Skke.i in Bøhmen (Jahrb. 



d. K. K. Geolog. Reichsans». 1895, Bd. 45 pag. 551. 

 ■- W. C. Brøgger : Om Paradoxidesskifrene ved KrekJinj. (Nyt. Mag. t. Naturv. 1878. 



Bd. XXIV, p. 56, tab. III, fig. 13). 



