San Mateo, Calif. -- Guidewire Software, a San Mateo-based maker of core system software for the insurance industry, on Thursday priced a follow-on offering expected to generate $226 million. The offering includes 8 million shares -- 7.3 million being sold by current shareholders -- for $28.25 each. The company, itself, is expected to make $19.8 million from its 700,000 shares offered. The news comes three months after Guidewire raised $115 million in its initial public offering (IPO). The company counts more than 100 property and casualty insurers among its clients, including GEICO, Nationwide and CNA.