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I found this Coenholectypus echinoid in the Mainstreet Limestone in Fort Worth, Texas. Unlike the heart-shaped echinoid that I've found in other formations, these type echinoids' tests appear to have fossilized into a dark crystalline mineral. I'm not quite sure what mineral this is, and hope that it doesn't react to acids so that it can be acid prepped. It can be hard to see in the image, but on the edge of the fractured test you can see that it's made of a dark mineral with a reflective shimmer. I'm not sure if it is just calcite with impurities to make it that color, but of the 5 specimens of this genus, the 3 that are also crystalline have the same coloration.

A short compilation of a quick jaunt into some lower Main Street Limestone (Upper Albian) exposures while doing botany work (my main focus) in the adjacent uplands yesterday, October 3rd. This creek bed exposes the lowermost ammonite zone of the Main Street, the Mortoniceras rostratum Zone (per Kennedy et al., 2005) Some of the abundant index fossil for this zone, the widespread Mortoniceras rostratum. Though most of these specimens are obscured by limestone matrix, all have at least the basal remnants of the characteristic rostrum of this species: Next, a nice small Peilina quadriplicata oyster with both valves preserved. This specimen is quite weathered in comparison to past material of P. quadriplicata I’ve collected but this species is always a pleasure to find: From a bit higher in the formation, a small but dense death assemblage block containing Neithea texana, Neithea wrighti, many Plicatula, abundant Cribratina texana forams, and various other things to be examined under magnification later: Lastly, a wonderful Symphyotrichum oblongifolium growing on the surrounding limestone slope barrens:

This last Sunday, I decided to dedicate the afternoon to scoping out a couple of prospective Woodbine sites and eventually make a return to my Pawpaw/Mainstreet spot from my most recent post. Unfortunately, the two Woodbine sites were complete duds. I left the high ninety degree weather with nothing but a tan. Thankfully, I saved the best site for last, so I was hopeful that my luck could still turn around before the sun left the sky. Things started off not being so productive. It was just rock after rock with the occasional concretion stealing away my attention. I was directing most of my focus to the smaller side of things as I was looking to find a complete specimen of my favorite ammonite genus, Engonoceras. About halfway through the hunt, I came across two interesting finds from the Mainstreet Limestone. The first was a Mariella heteromorph ammonite (A) that was better than the one I had come across last week. The second piece was unrecognizable to me at first glance. Its obvious symmetry is what initially caught my eye, but the long and slender figure was perplexing. After dusting it off a bit, I noticed the hinge that gave it away as a bivalve (B). I have never found a clam with such exaggerated features. With a little research, I have come to the possible ID of it being from the genus Arca, but I would love to hear what the invert experts have to say. After pocketing these, I really made an effort to focus on the smaller things in order to not come out of the day with my original goal unfulfilled. Just when I was beginning to feel sorry for myself and call it quits, there it was (C). Gleaming in the light of the setting sun was the bronze shell that had eluded me for so long. To say I was in disbelief would be an understatement. I probably could've milked the moment a bit more, but I was reaching down and picking it up before I could even stop myself. Suffice it to say, the juice was well worth the squeeze! Here are the pictures: A). Mariella heteromorph from the Mainstreet Fm. B). Arca texana? clam from the Mainstreet Fm. C). Pyritic micromorph Engonoceras serpintinum from the Pawpaw Fm. If you would like any additional pictures, let me know. Thanks for reading!