362 L. F. Spath — Jurassic Ammonites from East Africa. 



indeterminable Cephalopod remains so far have been recorded from 

 its rocks. It is interesting to note that six out of seven specimens 

 described in the present j^aper belong to the long-lived and stable 

 genera Phylloceras and Lytoceras, giving the fauna a typically 

 Mediterranean aspect. The influx of this Mediterranean fauna must 

 have occurred along the geosynclinal extension of the Tethys, 

 which has been called the "' Channel of Mozambique ". This geo- 

 synclinal, before the Bathonian transgression, apparently had not 

 attained the edge of the present African continent. A Sonninia 

 and a Parkinsonia, but no Phylloceras or Lytoceras have been found 

 in the Bajocian of Madagascar, but no pre-Bathonian ammonites 

 occur on the African continent west of this geosynclinal. 



Hecticoceras is found in North-West Europe and in the boreal 

 Callovian as well as in Alpine-Mediterranean deposits. On the other 

 hand, Phylloceras and Lytoceras have been found in Alaska, though 

 there also they are claimed to be confined to a geosynclinal 

 extension of the Mid-Pacific (which latter enabled the exchange of 

 the Spiti and Andine faunas). Professor Haug's conception of 

 Phylloceras and Lytoceras as stenothermal genera, frequent only 

 in the deej)est parts of the geosynclinal areas, does not explain all 

 the facts of their distribution. In a previous paper the writer 

 favoured the view that like other thin-shelled organisms, but unlike 

 many other Ammonites and Nautiloids, Phylloceras and lyytoceras 

 may have been pelagic swimmers, and thus in their distribution 

 show a certain dependence on the currents of the Jurassic seas. 



EXPLANATION OF PLATE V. 



Fig. L — Phijlloceras aPf. Kudernaischi (Hauer). Mombasa Pipe-line, at 



mile -5-. (x about LL) la, lateral aspect; 16, sectional outline; 



Ic, suture-line ( x about 3). 

 Fig. 2. — Phylloceras sp. ind. West of Mwachi River, about ^o^. Nat. size. 



2a, lateral view ; 26, outline-section ; 2c, portion of suture-line 



( X about 3). 

 Fig. 3. — Phylloceras cf. Kunthi Neumayr. Mwachi River, Pipe-line Crossing. 



Nat. size. 3a, lateral aspect ; 36, peripheral view ; 3c, suture-line 



( X about 5). 

 Fig. 4. — Phylloceras cf. disputabile Zittel. Mombasa Pipe-line, mile ii. 



4a, lateral aspect ( x about 1"1) ; 46, opposite side, showing constrictions, 



with restored outline of complete shell, nat. size ; 4c, outline-section of 



whorl, magnified x 2 ; 4d, suture-line (portion) x about 6. 

 Fig. 5. — Sowerbyceras aff. tortisvlcato d'Orbigny sp. Same locality as last. 



5a, lateral aspect ( x about LI) ; 56, outline-section, magnified x 2. 



5c, suture-line, composite and not drawn from one septal edge. 

 Fig. 6. — Protetragonites cf. tripartitus (Raspail). Mwachi River, Pipe-line 



Crossing, about -„-• 6a, lateral aspect, magnified x 2 ; 66, section ( x 2) ; 



6c, suture-line, external and internal ( x about 7 "5). 

 Fig. 7. — Hecticoceras sp. juv. Same locality as last. 7a, lateral aspect ( x 2) ; 



76, peripheral view ( x 2) ; 7c, suture-line ( x about 9). 



