William Shatner

,

priceline.com's

(PCLN)

celebrity spokesman, can not be pleased. After all, the former

Capt. Kirk

saw priceline's shares -- not to mention his own net worth -- beam sharply downward today.

A huge selloff followed the e-commerce company's announcement that third-quarter revenue will fall below analysts' expectations due to weakness in its main airline ticket business. priceline's stock tumbled $7.89, or 42.3%, to $10.75.

The online retailer forecast revenue of between $340 million and $345 million, compared to the $360 million to $380 million anticipated by analysts. priceline said a $20 million to $25 million shortfall in September airline ticket revenue -- due to a lower average offer price and a decreased number of accepted offers -- was responsible for the sales shortfall. Airline-imposed fuel surcharges, flight cancellations and the airlines' own sale fares were to blame, the company said. (

TheStreet.com's

Katherine Hobson

discussed

priceline's warning in another article.)

Investors have become all too familiar with profit warnings over the past couple of weeks -- with New Economy names

Viant

(VIAN)

,

PSINet

(PSIX)

, and most notably

Intel

(INTC) - Get Report

announcing shortfalls. (

TSC

is tracking September's

earnings warnings in a separate story.)

Third-quarter corporate confessions have had a domino effect on Wall Street, causing entire sectors to fall on the heels of one component's bad news. Today it was the Net names.

TheStreet.com Internet Sector

tanked 45.33, or 6.13%, to 694.51.

Despite the fact that

Yahoo!

(YHOO)

is a very different bird than priceline, shares of the Internet bellwether dropped $12.06, or 11.78%, to $90.38 alongside priceline.

Concerns about the flagging market for online advertising have hurt the Internet portal's stock over the past few weeks. Last month,

TST Recommends

Lehman Brothers

analyst Holly Becker said that it was only a matter of time before the slowdown in dot-com spending would affect Yahoo!'s results. An article shortly thereafter in

The Wall Street Journal

echoed Becker's worries that the tech bellwether will suffer from a slowdown in online advertising.

priceline's news also spread to online advertiser

DoubleClick

(DCLK)

, which fell $2.44, or 6.71%, to $33.88. Even a reiteration from

Credit Suisse First Boston

analyst Richard Petersen of a strong-buy rating was not enough to keep that stock above water. In his note, Petersen touted DoubleClick's announcement on Monday to purchase online research firm

atPlan

(APLN)

for $120 million in cash and stock.

In his report, Petersen wrote, "We believe the acquisition will help DoubleClick win business from larger, traditional advertisers who require market research tools and data to support their online marketing efforts." But today was not the day to rally the troops on behalf of Internet stocks.

Web issues

Amazon.com

(AMZN) - Get Report

and

eBay

(EBAY) - Get Report

lost 4.72% and 10.17% respectively.

Internet incubator

CMGI

(CMGI)

-- which announced last Thursday that it plans to take

AltaVista

search engine public by the end of October -- shrinked $3.19, or 12.53%, to $26.63.

Meantime, software company

BroadVision

(BVSN) - Get Report

-- initiated by

UBS Warburg

as a strong buy -- fell $1.81, or 6.17%, to $27.56.

With only two days left in the quarter, New Economy investors can only hope they've seen the worst and that the best -- meaning good earnings reports -- are yet to come.