On some New Species of Crustacea from the Upper Silurian Rocks of Lanarkshire &c.; and further observations on the Structure of Pterygotus

Abstract

A mong the rich collection of fossil Crustacea from Logan Water, exhibited by Mr. Robert Slimon at the Meeting of the British Association at Dundee, in September last, were several new forms belonging to the order Merostomata, which have since been acquired by the British Museum. 1. The first new form is represented (Pl. IX. fig. 1) by (1) an almost entire individual, measuring 11 inches in length and 5 inches in breadth, having one entire swimming-foot and three pairs of palpi in situ , and presenting the dorsal aspect of the body to view. (2) I met with a second example of this species in the Museum of Practical Geology, Jermyn Street (see Pl. X. fig. 2). It consists of the anterior part of an individual about the same size as that first mentioned, exhibiting, in situ , the ventral aspect with the postoral plate or metastoma ( m ), the bases of the swimming-feet ( e, e ), three pairs of perfect palpi ( b, b ), and the basal joints of what may perhaps prove to be two anterior organs corresponding, in position, to the antennæ ( a, a ). (3) I consider the detached organs and fragmentary remains figured on plates x., xi., and xiii. of Monograph I. of the Memoirs of the Geological Survey to be, in great part, referable to a species very closely allied to that from Logan Water. (4) I am enabled to figure a very fine lip-plate, obligingly left for my examination some time since by Mr. J. W. Salter, F.G.S., which