Clearing is what is done when A buys stock from B (or viceversa) by means of an intermediary (the brokerage house), since no one can just come in an trade in an exchange. Brokerage houses have mututal credit lines which operate in these transactions, so the clearing house (or agent) validates who did what in a given session and assigns the assets accordingly. Brokerage houses can also be clearing agents.
I envy your text!
Claudia

This text would indicate that the TA is the persons who 'transfers', which is not necessairly the person who 'clears'

EXTRACT
In the most straightforward bearer certificate protocol, *****the issuer and transfer agent (the same entity, for our purposes, though they can easily be unbundled)**** create a serial number (really a large unguessable random number, rather than a sequence), and add it to a list of issued certificates. The transfer agent clears a transfer by checking the signature to identify and nature of the bearer contract and verify that it was made, then looking on that contract's issued list to make sure the serial number is there, then removing the serial number. Alternatively, the issuer can let the issuee make up the serial number, then, when cleared, check the signature and put the number on the list of cleared certificates. The signature provides the assurance that the certificate is indeed the the particular kind of contract with bearer, while the serial number assures that the same instance of that contract is not cleared or redeemed more than once. In these simple versions, the transfer agent can link the transferee to the transferor for all transfers. To implement the privacy characteristics of coins and physical bearer certificates, we need to add unlinkability features.

FROM
http://www.google.com/search?q=cache:www.best.com/~szabo/for...

agente de traspaso: sinonimo - agente de transmisiones. Es la persona fisica o moral responsable de registrar los nombres y las tenencias de los propietarios de valores registrados, agregar el sello oficial y entregar los valores a los nuevos propietarios.

Suerte y Saludos!
Liliana