76 REPORT — 1856. 



The collections made by the Scottish geologists, — those in Lord Kinnaird's cabinet, 

 and in the Watt Institution, Dundee, — in connexion with other specimens obtained 

 by Mr. Banks of Kington and Messrs. Lightbody and Cocking of Ludlow, show that 

 that Pterygotus was an elongate crustacean, with a comparatively small head and 

 sessile compound eyes ; and having but few appendages, of which the large chelate 

 antennas are most remarkable, being a foot long, and only four-jointed, — the terminal 

 joints forming a strong serrated claw. The large mandibles were fully six inches 

 long: the maxillfe were either one or two pairs, with six-jointed palpi ; and the great 

 swimming feet consisted of six joints, of which the terminal ones were modified for 

 swimming; the basal joints are great foliaceous expansions with crenulate edges, which 

 possibly' assisted, like the first joints of the legs in Limulus, in mastication. 



The singular piece called " Seraphim " by the workmen, is not, as formerly sup- 

 posed, a portion of the carapace, but in all probability the hypostome on the under 

 side of the front of the head, the central prong of which is really free, being the labrum 

 itself. The plate would be analogous to a similar piece on the under surface of the 

 head of the Trilobite, — of Apus, Limtdus, and many other Crustacea. No argument 

 seems necessary to show that it was not a portion of the upper surface, as indicated 

 by Mr. Page in his communication to the Section last year, since we possess the cara- 

 pace entire, and it is like that of all the other nine or ten species. 



From the explanation given by Mr. Huxley in the memoir above referred to, there 

 is a general resemblance both in form and structure to the small Stomapod Crustaceans, 

 Mysis and Cnrna, minute forms, which are now arranged very low down among the 

 Decapods, and which are frequently ornamented with a sculpture very similar to 

 that of the fossils. There is even a yet greater resemblance in form to the larvae of 

 the common crab. If this be accepted, the coincidence in essential structure between 

 such minute and embryonic forms and these gigantic denizens of the old seas be- 

 comes. most remarkable and interesting, as bearing on the course of development of 

 life throughout geological epochs. 



On some New Palceozoic Star-fishes, compared with living Forms. 

 ByJ.W. Salter, F.G.S. 



The object of the communication was chiefly to exhibit some new forms oi Asteri- 

 dce, from the Upper Silurian rocks ; and others which have all the aspect of Ophiurida:, 

 but are essentially distinguished by the number of ossicles which go to form a single 

 segment of the arms — the lower surface showing a double row of flat plates, and the 

 upper also being composed of two rows of plates, while the Ophiuridce have a single 

 plate above, and one below. 



There is, however, the closest similarity to the latter family in the length of the 

 arms and the restriction of the disc (Protdster, Forbes)*. 



The Star-fish proper belong to three and probably to more genera, all remarkable 

 for their membranous texture. 



In the great length of the spines on the margin, Palaocoma resembles Pteraster, 

 MiilL, while in the pentagonal form and simply plated integument of another genus 

 {Palasterind), there is a much nearer approach made to Asteriscus or Palmipes than to 

 any other type of living star-fish. One of the latter had been described from Sweden. 



A Lower Silurian form, originally described by Forbes as Uraster, has the disc 

 little developed or quite absent, but better specimens show it to have had but two rows 

 of suckers, and the avenues bordered by very large plates. This is also appai'ently 

 allied to Asteriscus, and I find that the name Palceaster has been proposed by Prof. 

 Hall for the genus, which is represented by five or six species. 



The genera are, — 



1. Palaeaster {Hall), without disc, avenues deep. Upper and Lower Silurian . . 6 sp. 



2. Palasterina (M'Coy), pentagonal, disc moderate, plated. Upper Silurian , . 2sp. 



3. Palseocoma (5'a/<er),disclooselyreticular,avenuesveryshallow. Upper Silurian. 5 sp. 



4. Protaster (Forbes), disc small, arms long, extended, with two plates above 



and two below. Upper and Lower Silurian 4 sp. 



There appear to be other forms yet undescribed. 



* Later observations (1857) have led the author to believe this genus to be a true Ophi- 

 urid, but of a new group. 



