摘要：Early ontogenetic stages of some Ammonitina (mostly Perisphinctidae) are described from the Oxfordian Jagua Formation of western Cuba. Fourty six percent of the sample are specimens attaining the nepionic swelling with morethan four septa developed. Juvenile jaw apparatus found for the first time in specimens with only 2,25 whorls,displays primitive elements corresponding to conchorhynch and rhyncholit of nautiloids,litoceratids and phylloceratids. Thefauna and sediment features evidence a low water energy and low oxigenated conditions at the bottom during the sedimentation. The juvenile ammonites occur together with numerous adults which are represented by corresponding micro- and macroconchs: it indicates for the proximity of a breeding place.
其他摘要：W ciemnych konkrecjach wapiennych z formacji Jagua zaliczanej do oksfordu srodkowego,w prowincji Pinar del Rio w zachodniej Kubie,wystepuja masowo mikroskopijne muszle amonit6w obok duzych,czesto doroslych form. Na podstawie wyrazne] dominacji przedstawic
