Thanks to all! Especially gaffy for the inscription. Still don't have Jane's maiden name, sandiep. But that's a lot of McDowells that I hope are kin of mine.
So far the hope that they are kin depends on my theory that what was called Main Street in Antrim became High Street some time between 1870 and 1877 (I hope after Jane died in 1871). In the Belfast and Ulster Province Directory for 1870 there are no traders etc. on High Street, and many on Main Street. In the 1877 Directory there are many on High Street, none on Main Street, and many of the names that were on Main Street are now on High Street. They can't all have moved. The clincher is Mrs McNally, Massereene Arms Hotel, Main Street in 1970 and High Street in 1877; surely the hotel didn't move, it was just that its address changed.
So my hope about Jane is that she died at what was later called 45 High Street, residence of (I hope) her brother-in-law John McDowell, sewed muslin agent, who died there in 1886. So James Junior is John's brother, and James Senior is his father.
Too far-fetched?