In afternoon trade, the S&P/ASX 200 Index (ASX: XJO) is on course to record another gain. At the time of writing, the benchmark index is up 0.5% to 7,863.6 points.

Four ASX shares that have failed to follow the market higher today are listed below. Here's why they are falling:

The Cardno share price is down 46% to 33 cents. This has been driven by the professional infrastructure and environmental services company's shares going ex-dividend this morning. Last week, the company announced plans to distribute an unfranked dividend of 27.6 cents per share to shareholders. This equates to a total return of $10.8 million. This reflects the repatriation of US$5.9 million of collections related to three positive legal claims and $1.5 million from the sale of Cardno International Development to DT Global Australia. This dividend will be paid to eligible shareholders later this month on 29 April.

The Mesoblast share price is down 2.5% to 88.7 cents. This is despite there being no news from the allogeneic cellular medicines developer. However, it is worth noting that its shares have been on fire in recent weeks, so profit-taking could be happening today. For example, Mesoblast's shares remain up approximately 175% since this time last month. This has been driven by excitement over recent correspondence from the US Food and Drug Administration. Investors appear optimistic that one of the company's stem cell therapies could be approved at long last in the near future.

The Perseus Mining share price is down 2.5% to $2.27. This morning, the gold miner announced that its takeover offer for Orecorp Ltd (ASX: ORR) has been given a boost. Perseus revealed that Silvercorp Metals has accepted the company's offer. This is a big win as Silvercorp's holding represents 15.61% of OreCorp shares on issue. This means that Perseus now has a relevant interest of 74.98% of OreCorp shares on issue. However, it seems that investors don't appear overly keen on the proposed takeover.

The Somnomed share price is down 47% to 20.5 cents. Investors have been hitting the sell button in response to an earnings downgrade and capital raising. Somnomed downgraded its revenue guidance to 6%-9% growth and EBITDA guidance to negative $1 million to $0 million. This compares to previous revenue guidance of 12%+ and EBITDA guidance of $3 million+ for FY 2024. Management blamed manufacturing constraints and delayed implementation of cost initiatives. It also raised approximately $5.8 million at a deep discount of 21 cents per new share.