M. K. A. Zittel on Fossil LitMstidce. 467 



or rather angles, which, however, vary much in size,' rostrum 

 very prominent. Anterior legs in male large, equal ; hand 

 and wrist much swollen, fingers curved and armed with hairs 

 along their inner margin ; in the female these legs are slight 

 and their fingers almost straight. Ambulatory legs very flat; 

 anterior margin of first joint produced so as to form a very 

 prominent point, almost a spine ; claws half the length of 

 preceding joint. Whole animal destitute of hair, except on 

 the fingers. First and second pairs of ambulatory legs very 

 long, more than twice the length of the carapace. Breadth f 

 inch, length |-. 



Hah. Wellington. 



LIII. — Studies on Fossil Sponges. — II. Lithistidce. 

 By Kael Alfred Zittel. 



[Concluded from p. 894.] 

 Family 4. Tetracladina. 



AuLOCOPiUM, Oswald, 1846. 



(Schles. Gesellsch. fiir Taterl. Cultur, 1847, p. 58 ; F. Romer, Foss. 

 Faima von Sadewitz, 1861, p. 2.) 



Sponge free (not attached), hemispherical, rarely globular 

 or top-shaped, with impressed central cavity ; lower surface 

 coated with a wrinkled dense siliceous membrane. From the 

 lower extremity of the central cavity numerous water-canals 

 radiate to the periphery ; curved canals of larger diameter, 

 parallel to the contour line, open into the stomachal cavity. 

 Skeleton formed of smooth, irregular, quadriradiate elements, 

 each ray branched root-like at the end. These are usually 

 arranged in rows so that the ramified ends of two neigh- 

 bouring rows meet in a plane parallel to the radial canals, 

 greatly enhancing the radiate appearance seen in a transverse 

 section of the sponge-body. 



The Aulocopia occur as chalcedonic pebbles in the North- 

 German diluvium, especially on the island of Sylt. The 

 microscopic structure is then generally well preserved, and 

 may be shown in thin slices. In other places, as at Sade- 

 witz, the whole sponge is filled with calc spar, and the origi- 

 nally siliceous skeleton converted into calc spar. The same 

 unfavourable conditions prevail in specimens obtained in 

 situ from the Silurian beds of Esthonia, sent by Prof. F. 

 Schmidt of St. Petersburg. In those from Sadewitz the 



31* 



