. Bulletins of American paleontology. ores havebeen diagrammed in this way, and all have yieldedinterpretable stories of the evolution of various partsof the Bay. MISCELLANEOUS OBSERVATIONS Precocious Maturity As mentioned above. Durbin Tabb told me manyyears ago how Transennella responds to changes insalinity by maturing quickly and reproducing beforethe onset of an unfavorable environment causes itsdeath. His comment led me to wonder whether thiswas an isolated phenomenon in this pelecypod or amore general molluscan characteristic. Transennella does not show distinctive physicalsigns of sexu
. Bulletins of American paleontology. ores havebeen diagrammed in this way, and all have yieldedinterpretable stories of the evolution of various partsof the Bay. MISCELLANEOUS OBSERVATIONS Precocious Maturity As mentioned above. Durbin Tabb told me manyyears ago how Transennella responds to changes insalinity by maturing quickly and reproducing beforethe onset of an unfavorable environment causes itsdeath. His comment led me to wonder whether thiswas an isolated phenomenon in this pelecypod or amore general molluscan characteristic. Transennella does not show distinctive physicalsigns of sexual maturity on its shell, but some pelec-ypods and many snails do. Therefore, if the ability tomature precociously is generally present among mol-lusks we should find both large and small shells show-ing these mature structures. The first shell for which 1 found both large andsmall mature shells was the snail Cerirliidea. Its ma-turity is signaled by a flaring of the aperture outwardfrom the earlier plane of the shell. Text-figure 37. Text-fiiiurc .^S.—Pre ty: Ceritluopsis gr shows two mature shells: the one on the left is tall while that on the right is only mm. Text-figure 38 shows another gastropod, Cerithiop-sis greenii. This is a smaller shell in which maturitymanifests itself by a narrowing of the final whorl. Theshell on the left is mm. tall, while that on the rightis only mm high. Mature shells taller than mmwere seen during the study. Even the tiny shells of Caecum, in which maturityis expressed by a narrowing of the apertures at themouth of the shell, show this same characteristic. This is not the place to pursue this idea at length,but it has some implications for molluscan also bears on the origin of some enigmatic assem-blages, known as dwarf faunas. These are made upmainly or entirely of minute but fully formed shellswhose origin has long been a paleontologic puzzle. Postmortem Shell MovementWhen I originally undertook this stu
Size: 1485px × 1683px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookidbulletinsofa, bookyear1895
