Post by Paul on Nov 4, 2005 21:13:27 GMT
I thought cross-weave would make the most sense.
from Bequaert....
"Two main features distinguish the several variations of A. marginata from the related members of the genus. The first is subsutural, usually strongly marked engraved line, separated from the suture by a low narrow depressed area covered with irregular, low, vertical folds, the suture itself being straight or very slightly wavey, not crenulate. The engraved line starts on the fourth and fifth whorl and it is often deep and prominent, particularly on the body-whorl; but occasionally it is weak or almost lacking, especially in subsp. eduardi Pilsbry. The second feature is a peculiar microsculpture of the body-whorl, only visible with the proper magnification. It consists of numerous extremely fine, close-set, criss-cross or anatomising lines, making the surface of the periostracum look as if it had been pressed with a very finely woven cloth. This "weave" type of microsculpture is more pronounced in some forms or races than in others. It is particularly conspicuous when the periostracum is well developed and preserved, as is more common in some of the Cameroon races, such as subsp. egregia. In old shells, even when taken alive, the microsculpture is sometimes almost completely worn off, but traces of it may generally be detected in a few spots. The nepionic whorls, when well preserved, as in newly hatched or very young shells, are densely covered with regular spiral and vertical rows of minute granulations, which become coarser on the first, post-nepionic whorl."
The picture showing this is X 2.
It is not too clear about whether it develops with age or size. As for chubbs, he does mention that a particular specimen had to be ventricosa speculatum because the shell was much too wide for purpurea. So purpurea seem to be less ventricose. Not sure how that helps exactly, but I was thinking if his shell is quite bulbous and margie-like in shape, it is likely to be a ventricosa speculatum as Mike deduced.
Incidentally, whilst in a lot of cases Mike is correct about colour developing with age, Bequaert says that a lot of species lose the colour with age, for instance A. balteata loses its columella colour with age.
from Bequaert....
"Two main features distinguish the several variations of A. marginata from the related members of the genus. The first is subsutural, usually strongly marked engraved line, separated from the suture by a low narrow depressed area covered with irregular, low, vertical folds, the suture itself being straight or very slightly wavey, not crenulate. The engraved line starts on the fourth and fifth whorl and it is often deep and prominent, particularly on the body-whorl; but occasionally it is weak or almost lacking, especially in subsp. eduardi Pilsbry. The second feature is a peculiar microsculpture of the body-whorl, only visible with the proper magnification. It consists of numerous extremely fine, close-set, criss-cross or anatomising lines, making the surface of the periostracum look as if it had been pressed with a very finely woven cloth. This "weave" type of microsculpture is more pronounced in some forms or races than in others. It is particularly conspicuous when the periostracum is well developed and preserved, as is more common in some of the Cameroon races, such as subsp. egregia. In old shells, even when taken alive, the microsculpture is sometimes almost completely worn off, but traces of it may generally be detected in a few spots. The nepionic whorls, when well preserved, as in newly hatched or very young shells, are densely covered with regular spiral and vertical rows of minute granulations, which become coarser on the first, post-nepionic whorl."
The picture showing this is X 2.
anjieburdett said:
The inside of the shell lip on Chubbs is dark purple/deep pink...but do Purpurea/Ventricosa var. Speculatum not get that until they are older?? Is that what you mean Paul? It is not too clear about whether it develops with age or size. As for chubbs, he does mention that a particular specimen had to be ventricosa speculatum because the shell was much too wide for purpurea. So purpurea seem to be less ventricose. Not sure how that helps exactly, but I was thinking if his shell is quite bulbous and margie-like in shape, it is likely to be a ventricosa speculatum as Mike deduced.
Incidentally, whilst in a lot of cases Mike is correct about colour developing with age, Bequaert says that a lot of species lose the colour with age, for instance A. balteata loses its columella colour with age.