Compare and contrast the various types of secondary market trading structures. 

Answer:  There are two major types of secondary market trading structures:  dealer and agency.  In a dealer market, the dealer works like a market maker for the security, holding an inventory of the security.  The dealer buys at his bid price and sells at his inquired price from this inventory.  All public trades undergo the dealer.  In an agency market, public trades undergo the agent who matches it along with another public trade.  Both of the dealer and agency markets can be uninterrupted trade markets, but non-continuous markets tend to be only agency markets.  Specialist markets, Over-the-counter trading, and automated markets are types of continuous market trading systems.  Call markets and crowd trading are every types of non-continuous trading market systems.  Continuous trading systems are wanted for actively traded issues, while call markets and crowd trading present benefits for smaller markets with many thinly traded issues as they mitigate the possibility of sparse order flow over short time periods.