. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Middle Pexnsylvaniax Pelycosaurs • Reisz 51 Tlie ends of the centra are formed in such a manner that there are huge intercentral spaces ventrally. Dorsally the anterior and posterior ends of the centra touch. This t\pe of be\ening for the intercentra is prob- ably ven- priniiti\"e, and is seen in some \'ery primiti\e romeriids (Carroll, 1970: fig. 8f). The intercentra are well devel- oped, but do not show the lateral facets where the capitulum would be expected to articulate. The nature of the intercentral spaces
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Middle Pexnsylvaniax Pelycosaurs • Reisz 51 Tlie ends of the centra are formed in such a manner that there are huge intercentral spaces ventrally. Dorsally the anterior and posterior ends of the centra touch. This t\pe of be\ening for the intercentra is prob- ably ven- priniiti\"e, and is seen in some \'ery primiti\e romeriids (Carroll, 1970: fig. 8f). The intercentra are well devel- oped, but do not show the lateral facets where the capitulum would be expected to articulate. The nature of the intercentral spaces suggests that the intercentra had cartilaginous d(;rsal extensions. The transverse processes have the type of webbing seen in typical ophiacodonts; li()\\('\-er, it does not extend as far \-entralK- as in other members of the family. Dorsally, the articulating surface of the transxerse process is not as rounded in section as in other ophiacodonts. The zxgapophyses, which extend far beyond the anterior and posterior margins of the centrmn, are mod- erately tilted. The angle of this tilt is estimated to be more than 35 degrees, a con- dition seen in sphenacodonts. The zygapo- physes are close to the midHne. The neural spines are different from the type usually seen in peKcosaurs. They are only 5 mm high, yet are extremel)' wide. At the base they are mm wide; dorsally they con- strict to mm and then expand again to become as w ide at the top as they are at the base. Although the specimen shows some primi- tive as well as ophiacodont and sphenaeo- doiit eliaracters, the determination of its exact taxonomic position among pelycosaurs has to await the discovery of more complete specimens. II. Eight caudal vertebrae (Fig. 14) are found in block B (MCZ 4095). The centra are massive structures solidly fused to the neural arches. The anterior and posterior articulating surfaces of the centra are strongly developed and on the \entral re- gion there is marked bevelling to accomm
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