Before 2018 runs out, a trip to the lab to prepare this semi-prone Asaphus lepidurus, the more common asaphid found in the St Petersburg, Russia quarries. Also, a new trilobite addition.
This is what it looked like before starting. The pleural orientation makes it clear that the cephalon will be projecting downward as this bug was buried in the process of enrolment. There is some damage to the final pleural segment before the pygidium. The initial challenge was getting rid of the tall stack of matrix on top of the bug using only my ARO clone with factory tip.
The GIF above shows the process after four hours of scribing and abrading. You know those preps of Russian trilobites with the soft and easy matrix due to marl content, the stuff that comes off like butter? -- Yeah, this isn't one of those. Instead, the matrix is hard with calcite crust. It is the kind of stuff that you can't risk getting too close with the scribe for fear of dinging the bug (or drilling through!), and the stuff that laughs at the air eraser even cranked up to 75 PSI. Even pin vise pricking is not able to gain enough purchase to separate matrix from shell. I'm going to have to risk approaching it blind from the anterior side in the hopes that I can locate the cephalon, working my way out and eventually freeing the left side pleurae.
The orientation is not the easiest to work with. Being semi-prone means the pleural segments tend to bunch together and are a bit more fragile... One misstep means losing shell pieces. By contrast, the axial rings are stretched out to their maximum convex flex, and that can lead to other problems such as shell thinness.
Four hours became eight hours. Eight became seventeen. The matrix was sticky and pretty much immune to dolomite abrasion. So it was the delicate and less than ideal process of using the vibrating scribe tip to "kiss" the matrix to cause it to flake off, and some matrix shaping to level down the bug's contours as well as expose the cephalon. The latter took a very long time. You can see the scribe dings in this image, but those are easy enough to fix. Now comes the finicky job of removing all the hard grit between the segments.
Success! The stubborn matrix grit is gone. The only disappointment is that this one seems to be missing the lowermost left pleural segment just anterior to the pygidium. I had been careful to level down slowly, so I didn't accidentally scribe it off; I think this is just moult-related damage, and that is made more likely by the slight misalignment of the pygidium in relation to the thorax. It happens!
Also missing a wee bit from its left eye, but on the whole a half-decent prep.
This delightful diminutive phacopid had come in the mail. From what I read, it was collected about 50 years ago from the classic "trilobite fields." Gerolstein, Eifel mountains in Germany, Ahrdorf Formation, Flesten Member. I'm told this site is no longer available for collecting, so makes this trilobite extra special. It measures just about 1 cm across the transverse axis.
While moving some spare rock from the living room to the basement where I keep my spoils, spare parts, and fossil graveyard, I decided to break open this big block I kept from my recent trip to Bowmanville. I managed to expose a bit more of this Isotelus fragment. Six out of the eight thoracic segments are visible and part of the pygidium. Had this monster been complete, it would have measured about 28 cm in dorso-saggital length! Apart from the rarity in finding such extra large isotelines, that is made more so by the fact that the very largest ones rarely preserve well being subject to more exposure, crush damage, etc. It is for that reason Dave Rudkin's team's find of that Iostelus rex in 2002/3 was such a coup (72 cm in length -- the biggest trilobite on record!). It is a bit tougher to make out the species on this one, but I'd wager this is likely an Isotelus latus. Now to wait until May to find a complete one!
But let me sneak in just one last prep before wrapping up the year. This is a
Flexicalymene croneisi that Deb found in Bowmanville in October, and I've been meaning to clean this one up. Pictured to the left is after I've done some preliminary work, and on the right is the complete deal. One hour prep. The pictures don't do it justice (it's still dusty and has some dolomite dust in the cracks, and the iPad is not the greatest for macro shots), but I'll take a better picture before putting it in the trilobite gallery.