332 SECTIONAL TRANSACTIONS.— D. 



Prof. Th. Mortensen. — The Geographical Distribution of the Cidarids 

 with special reference to South African and Antarctic Seas. 



A review of all the known recent forms of Cidarids, amounting to 150 (circa) species 

 and varieties, shows a very marked overweight of the Indo-Pacific Cidarid-fauna over 

 all other regions of the world. 



The Malay Archipelago, and particularly the Moluccan part of it (the ' Amboinese ' 

 region of Doderlein) has by far the greatest number of species (48) ; next comes Japan 

 with 26, the Indian Ocean with 21, and the Australian region with 18 species. In 

 marked contrast herewith we have in the whole of the Atlantic, including the West 

 Indies, ordy 16 species. During Mesozoic times Cidarids were extremely numerous 

 in the seas occupying the place of what is now ]\Iiddle and Southern Europe, about 

 600 species being known from these deposits, whereas there are now in the European 

 seas in all only 4 species, including those known from the N.E. Atlantic Deep-sea. 

 The explanation of this almost total disappearance of the former very rich fauna 

 may be sought in the decline of temperature, from the tropical conditions of the 

 Jurassic period to the arctic conditions of the Glacial Epoch. But the relative poverty 

 of the tropical parts of the Atlantic cannot be explained in this way ; it indicates that 

 the Atlantic is of comparatively recent origin, so that there has not been time enough 

 for the developing of a rich fauna. The theory of Wegener, of the Atlantic having 

 been formed through the American continent drifting away from the Eurasian-African 

 continent, or Ihering's Archelenis theory — the existence of a previous land-connection 

 between Africa and S. America — may account for the fact of the relative poverty of 

 the tropical Atlantic. 



The Antarctic Sea has a rather rich fauna of Cidarids, 16 species, all belonging to 

 a separate group showing several primitive features, this group being confined to the 

 Antarctic, with the sole exception of a couple of deep-sea species found in the Pacific. 

 It seems to indicate that the Antarctic Sea is a very old sea, in which this primitive 

 group has found conditions for a rich development, being there free of competition 

 of related forms. It seems to be a case analogous to that of the Marsupials of Australia. 



In close relation to the Antarctic stands the Magellanic region, whereas New 

 Zealand-Australia have no relation to the Antarctic as regards their Cidarids (and 

 Echinoderms on the whole) ; only one of the New Zealand Cidarids shows some 

 relation to the Cidarid characteristic of the Magellanic region, Austrocidaris 

 canaliculata, which again belongs to the group peculiar to the Antarctic Sea. To 

 this group also belongs a Cidarid found at Kerguelen and the adjacent islands. From 

 S. African seas is known with certainty only one species of Cidarids, but at least two 

 more appear to exist there ; they are all decidedly of Indo-Pacific origin ; with the 

 Magellanic or the Antarctic region the S. African region has no nearer relation, judging 

 from its Cidarid-fauna, and, indeed, from the whole of its Echinoderm-fauna. 



Prof. C. G. S. DE ViLLiEES. — The Development of a Jonlershoek Species of 



Arthroleptella with some remarks on the Affinities of the Genus. 



In November 1928 several adults and representative stages of the life-history of 

 Arthroleptella were procured in damp moss at Jonkershoek, SteUenbosch. The adults 

 are smaU dark frogs inhabiting moss, and are probably widely distributed in the 

 Western Province. They are preUminarily classed as Ranidae, but their develop- 

 ment is quite different, since it is of the non-aquatic type also found in the Brevicipitid 

 genera Anhydrophryne and Breviceps. The ova are rich in yolk, but telolecithaly 

 has not called forth meroblasty. The albumen capsules are partially adherent and 

 exceptionally large. The development of the gut from the yolk takes place in much 

 the same way as in the Brevicipitids mentioned. The respiratory system is of great 

 interest, since one pair of very small external gills only are developed and the internal 

 giUs are absent, although one branchial sac is present. The lungs cannot function 

 till late, because the gut is not in communication with the oral cavity. The larval 

 jaws and teeth, as well as the suckers, are absent. The pectoral girdle has arciferous 

 epicoracoids in the metamorphosing froglets. The sternum of the adult has sternal 

 sacs for the coracoids. A procoracoid is present, but there is no clavicle, as is some- 

 times stated. The scapula has a pronounced acromial process. The development of 

 the skuU has been traced, and the anatomy of the adult condition investigated 

 micro tomicaUy, special attention being devoted to the os en ceinture, paraquadrate 

 and quadrato-maxillary. The development and metamorphosis of the middle ear 



