Scale Counting Question

I almost hate to place this question in this category but there is not a General category for snakes, and this question applies in general to all snakes, so here goes:

How is a proper scale count done?


I picked up what was purported to be a Brazilian Rainbow Boa from a friend who wanted me to try and sell it at the White Plains Show last month. When it did not sell, I bought it. It is a nice healthy juvenile snake of good size, but I think it is a Peruvian Rainbow Boa based on a scale count I did and on information from The Rainbow Boa Page. I came up with 42 scales at mid-body, which according to info on The rainbow Boa Page means this is a Peruvian.

Yet I wonder if it matters that I counted from the ventral scales on one side straight across the back along a diagonal row to the ventral scales on the other side. I did it like /. I now wonder, was I supposed to hit the spine and then turn back as if counting along a > instead of a /? Since I counted twice, and my eyes really get strained doing this sort of thing, I am hopeful someone can tell me if I need to do it again, this time along a >, or if I did it ok the first time.

THANKS

Best regards,
Glenn B

Usually you are supposed to hit the spine and start counting back in the other direction in that > shape... or you can count in a zigzag straight up and over, although I've personally always thought that was a bit harder on the eyes

<
>
<
>

Pattern for the zigzag, back and forth up essentially two lines of scales.

But even if you counted forward in this / pattern straight over the spine, it shouldn't throw off the count by more than a few, if that.

Couple things to check would be:

1) Make sure the count was correct by doublechecking a few times. (You already did but it's good advice for anyone else)

2) Make sure the subspecific groupings only have one distinguishing scale count... I'm not sure what it is for Rainbows, but I know Boa constrictor ssp., you have to count a number of different scale groupings (Midbody, ventral, subcadual) and even then there's generally a small range that each subspecies will fall under, you just hope you have a count that rules out some of the subspecies.

3) If the bloodline has been captive for awhile or the origins can't be 100% pinned down, chances are fairly good it might be a subspecific cross, which throws all the scale counts out the window. Some scale counts end up being dominant (Like subocculars in P. molurus crosses) but most will end up a bit jumbled, taking different counts from the different subspecies in the lineage.

One of the easier to see visualizations for scale counts can be found in the Audubon societies reptiles and amphibians field guide if you have one laying around, if not I think I've probably got a few books around here with decent graphics that I can scan in and possibly post if it would be of any help.

It's just important to remember that scale numbers are a fairly minor genetic deviation and that most species and even many subspecies can have numbers between a certain range rather than an exact number and that anything that's been captive for a while (species-wise) is probably composed of mixed subspecies and locales, which screws up the counts unless you're dealing with veriviable and known imports from a source that keeps much more detailed records about collection data than most.