defendants are alleged to have participated in the issuance of a materially misleading Registration Statement and Prospectus. The plaintiffs allege that as a result of materially misleading statements and omissions in these documents, Diasonics’ common stock was traded at artificially high prices and that the plaintiffs were consequently damaged.
Both the plaintiffs and the defendants raise various motions. They are:
(1) plaintiffs’ motion to certify a plaintiff class;
(2) plaintiff Rothenberg’s motion to certify a separate section 10(b) class;
(3) plaintiffs’ motion to certify a defendant underwriter class; and
(4) defendants’ motions for partial dismissal (which includes several sub-motions).
FACTUAL BACKGROUND
Diasonics, a California corporation with its principal place of business in Milpitas, California, develops, manufactures, markets, and services medical diagnostic imaging systems. These sophisticated computer-based X-ray and ultrasound systems are used by physicians in hospitals, clinics, and private practice.
On February 23, 1983, Diasonics commenced its initial public offering of 5,588,-000 shares of common stock at an offering price of $22.00 per share. This public offering was made pursuant to a Registration Statement and Prospectus filed with the Securities and Exchange Commission, effective February 23, 1983. Plaintiffs allege that this Registration Statement and Prospectus were materially false and misleading. Specifically, plaintiffs contend that these documents overvalued Diasonics’ assets and understated certain delivery and sales problems.
On September 22, 1983, Diasonics first revealed through a press release that it expected a pre-tax loss of $10-14 million for the third quarter of 1983. This expected loss was attributed to a decline in the profitability of its ultrasound and digital X-ray business. On January 31, 1984, Diasonics revealed that it expected a total pretax loss of between $60-65 million for the year ending December 31, 1983.
Following these two disclosures, the value of Diasonics’ stock declined precipitously. By late September, 1983, following the first press release, the price of a share of Diasonics’ common was $9Vs bid; by February, 1984, the price had declined to between $4-5 per share.
The plaintiffs have now filed the instant action and allege various statutory and common law claims. In specific, the plaintiffs seek relief under: section 11 of the Securities Act of 1933, 15 U.S.C. § 77k; section 12(2) of the Securities Act of 1933, 15 U.S.C. § 111; sections 17(a)(2) and (a)(3) of the Securities Act of 1933, 15 U.S.C. § 77q; section 10(b) of the Securities Act of 1934 and Rule 10b-5, 15 U.S.C. § 78j(b); section 25400 et seq. of the California Corporations Code; and common law theories of fraud, deceit, and negligent misrepresentation.
DISCUSSION
I. Plaintiffs’ Motion to Certify a Plaintiff Class
The plaintiffs seek the certification under Fed.R.Civ.P. 23(b)(3) of the following plaintiff class:
All persons and entities, other than defendants, who purchased the common stock of defendant Diasonics, Inc. from February 23, 1983 through January 31, 1984, inclusive.
Certification of a class under rule 23 requires that the putative class meet the four requirements of rule 23(a) and that it qualify under one of the three subdivisions of rule 23(b).
A. Prerequisites under rule 23(a)
Rule 23(a) sets out the first aspect of class certification:
One or more members of a class may sue or be sued as representative parties on behalf of all only if (1) the class is so numerous that joinder of all members is