272 CONFERENCE ON PALEOZOIC PALEOGEOGRAPHY 



(may have representation in South Australia in Megerlia (?) wille- 

 moesi) . In common with this region and the northwestern side of Gond- 

 wana or the Antillean-Floridian and Caribbean area are the genera Cis- 

 tella, Eucalathis (1 species in the Fiji region), Platidia (has spread to 

 Lower California, but not to South America), and Thecidium. 



There are 9 other genera that must be considered in detail : 



Glottidia. — This genus had its origin apparently in the Antillean 

 region, spread north as far as North California, south to Martinique, and 

 in the Pacific north to southern California and south to Peru. The 

 genus is known in the Pliocene of California, and the spreading probably 

 took place previous to the upper Miocene when the Panama land bridge, 

 between North and South America, was established. Glottidia seems to 

 be not older than the Tertiary. 



Discinisca. — The genus is most abundant off the South American Pa- 

 cific, has spread north to the Gulf of California, and is sparingly present 

 in the Antillean region. A single species occurs from Singapore to 

 Japan. As the genus probably dates from the late Mesozoic we may have 

 here local continuance of a formerly much wider, now much broken and 

 discontinuous distribution. On the other hand, the present dispersal 

 may be due to larval transportation, for the larvae of the deep-sea Pelago- 

 discus (formerly called Discinisca) have been taken in the drag net very 

 far from land and are known to live in the free and floating condition 

 for nearly a month. 



Crania. — This genus is very common throughout the Paleozoic and 

 Mesozoic faunas of the northern hemisphere, and it is therefore probably 

 safe to assume that it originated here. In any event Crania is today most 

 abundant in northern oceans, where there are 4 species. In the southern 

 hemisphere there are 3 forms, 1 off southeastern Australia, 1 in Antarc- 

 tica, and 1 off western Patagonia. Its distribution seems to agree closely 

 with that of Terebratulina. 



Cryptopora has a greatly discontinuous distribution and may not owe 

 its present occurrences to Gondwana. It was originally described (C. 

 gnomon) from the north Atlantic, and is now known to be almost uni- 

 versal throughout the deep waters of this ocean from Davis Strait and 

 Tromso to off Morocco, the Azores, and the Canaries. The other form 

 (C. hrazieri) occurs in shallow water off New South Wales. 



Terebratulina probably originated in the northern hemisphere and is 

 known fossil since the Jurassic. Its greatest present specific development 

 is about Japan, where 6 forms are known. In the northern hemisphere 

 are living 11 species, against 3 in the southern hemisphere. In other 

 words, the genus is common to almost all shores in the northern hemi- 



