Green Dot Corporation (NYSE: GDOT) rose more than 27 percent in Monday's late session to $19.50. The bank holding company authorized a plan to buyback up to $150 million of its common stock and said it will continue to serve as the issuing bank for the Walmart prepaid debit cards.

Comstock Resources Inc (NYSE: CRK) rose about 5 percent in late trading to $4. The oil and gas company didn't issue news.

Humana Inc (NYSE: HUM) gained about 4 percent after the bell to $197.93. The shares closed down about 6 percent earlier. Aetna Inc (NYSE: AET) reportedly made an offer last week for Humana although details weren't disclosed.

Epizyme Inc (NASDAQ: EPZM) extended its gains, rising more than 2 percent to $26.57. The drug development company gained more than 25 percent before the bell on favorable data concerning Phase I data on its non-Hodgkin lymphoma treatment.

Peabody Energy Corporation (NYSE: BTU) picked up nearly 3 percent after the bell, trading at $2.70 a share. The coal company is off about 66 percent in the year-to-date and said Friday it will sell properties in Australia.

Calithera Biosciences Inc (NASDAQ: CALA) increased more than 2 percent to about $8.92 a share. The company didn't issue news Monday.

Sonic Corporation (NASDAQ: SONC) fell about 5 percent after Monday's bell to $32.40. The restaurant chain posted disappointing quarterly earnings.

PTC Therapeutics, Inc. (NASDAQ: PTCT) bounced down about 3 percent to $50.70. The biopharmaceutical company gained 6 percent before the bell and didn't post news.

Intevac, Inc. (NASDAQ: IVAC) gave back about 3 percent, trading at $5.83 after the bell. The company, which supplies manufacturing equipment to disk drive makers, gained 10 percent earlier Monday on no obvious catalyst.

Darden Restaurants, Inc. (NYSE: DRI) declined 2.9 percent to $67.35 in late trading. The company is set to post quarterly results Tuesday and didn't issue news.

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