MICRODISOUS PUNCTATUS. 39 



in regarding the two forms as identical. According to Walcott, Salter's figures 

 differ from the American specimens in having a longer and more slender spine, 

 and a punctate surface to the head and pygidium. Salter's fig. lib shows the 

 spine longer than it usually is, and Walcott himself in his description states that 

 the surface of the American form is finely punctate. 



There can now be little doubt that the species described and figured by 

 Matthew in 1886 as M. punctatus, Salter, var. pulchellus, Hartt, and in 1896 as 

 M. pulchellus, Hartt, is identical with M. punctata*. The characters on which he 

 relies to distinguish the American form are the smaller and more erect occipital 

 spine, the larger number of rings on the pygidial axis, and the fact that the tail is 

 tubercnlate instead of punctate. The spine in the Welsh form varies considerably 

 in length, and is often flattened down upon the thorax or broken away altogether ; 

 but external moulds show that it rose from the plane of the head at a considerable 

 angle, and it is not usually any longer than in Matthew's figure. The number of 

 rings on the axis is understated by Salter. In most well-preserved specimens of 

 the usual size eight or nine rings are quite distinct, and there may be indications 

 of others. Owing to the increasing vagueness of the annulations towards the end 

 of the axis the precise number of rings which can be counted is a character of 

 little value. As regards the ornamentation of the tail, it has been shown above 

 that owing to the peculiar structure of the test internal casts are often tubercnlate. 



The form referred by Whiteaves to M. punctatus appears to be the same as 

 Matthew's M. pulchellus. He states that the species has been observed "on the 

 Kennebecasis River, N.B., where it was collected by Mr. Gr. F. Matthew." This 

 is one of Matthew's localities for M. pulchellus. 



From a somewhat higher horizon than M. pulchellus Matthew describes 

 another form, which is distinguished by possessing a punctate tail, and which he 

 therefore identifies with M. punctatus, Salter. In one locality, however, from this 

 same horizon, specimens have been obtained with tuberculate tails. The difference 

 is probably due to the mode of preservation, the punctate specimens showing the 

 exterior surface of the test and the tuberculate specimens showing the interior. 



Types. — The original of Salter's fig. 11 c is in the Sedgwick Museum, 

 Cambridge; some artificial casts of his fig. 11 a are in the British Museum. Salter 

 states that there are four thoracic segments ; but the type specimen (re-figured in 

 Plate III, fig. 11) possesses only three. In this specimen, which is an internal 

 cast, the surface of the tail is tuberculate. 



Horizon and Localities. — Menevian : Porth-y-rhaw and Nine Wells, near 

 St. David's ; Dwrrhyd, near Solva; Tyddyngwladys, Upper Mawddach ; Waterfall 

 Valley, Maentwrog. 



