~ 11 — 



appear to exist. At present the results of the investigations of 

 the sponL;cs ot the Challenger expedition are not known, but 

 recent in\estigations of the Atlantic sponges by Mr, Carter 

 and those from the Gulf of Mexico by (Jscar Schmidt show that 

 the previous ideas as to the depth in which different orders of 

 sponges exist, ha\e to be considerably modified. The Mon- 

 actinellidae and Tetractincllidae were former!)' regarded 

 as inhabiting comparatively shallow waters, but it is now 

 ascertained that they extend to depths previously thought to be 

 exclusi\ely inhabited by Lithistidae and He.xactinellidae ; whilst, 

 on the other hand , some rcpresentati\es of these latter are 

 now known to exist in but moderate depths. Two or three 

 examples ma)' be gi\en of the depths in which existing 

 sponges nearly allied to those in the chalk, have been dis- 

 covered. i\ species of Pachastrella, /-*. aniygdaloidis^ Carter, 

 whose spicules most close])- resemble some in the Chalk flint, 

 exists in the Atlantic at a depth of 1752 feet; Lyidiinn 

 torquilla. O. Schmidt to which the chalk .spicules of the 

 same genus are nearly allied, also exists in the Atlantic, off 

 the coast of Cuba, at a depth of 1610 feet; Lithistid .sponges 

 nearly allied to Racodiscula occur at var)'ing depths between 

 720 feet and 1620 feet; the Hexactinellidac are most abundant 

 in depths between 1 800 and 6000 feet, but a species of 

 Cystispongia a genus also represented in the Chalk flint is 

 recorded by Oscar Schmidt (Spong. d. Meerbusen von Mexico) 

 as existing at depths varjing between 120 feet and 175- feet. 

 So far as these comparisons extend, the sponges of this 

 chalk flint may ha\e inhabited depths of 1700 feet. 



The great resemblance which is presented b)' these 

 Horstead sponge remains and the spicules which have been 

 described from the Haldon Green Sand; the Upper Chalk of 

 the North of Ireland, the Chalk Formation of Westphalia, 

 and the Eocene Sand of Brussels shows that these sponges 

 had a wide distribution both in space and time. In the 

 Eocene strata of Brussels there occur many forms of spicules 



